Based on distributed fiber optic sensors, fiber grating sensors and fiber interferometers have been widely used in tensile force measurement. In contrast, fiber interferometers have been widely studied due to their high sensitivity, such as Mach-Zehnder Interferometers (MZI), Fabry-Perot Interferometers (FPI), and Sagnac Interferometers (SI). On this basis, in order to improve the tensile force sensitivity of fiber interferometers, cascade fiber interferometers based on Vernier effect are proposed, such as cascaded dual MZI, cascaded dual FPI and cascaded MZI-FPI structures. However, the matching of the optical path difference and insertion loss of the cascade structure has always been a difficult problem to solve, which can affect the spectral quality of the Vernier effect. Therefore, the sensing accuracy and resolution of the tensile force measurements are limited.In this paper, a parallel FPI all-fiber tensile force sensor based on the Vernier effect is proposed, which is composed of a Sensing FPI (SFPI) and a Reference FPI (RFPI) in parallel. The structure is prepared only by an arc discharge technology, which ensures the uniformity and repeatability of the structure preparation. Among them, the SFPI is a closed air cavity. The tapered air microcavity is fabricated by precisely controlling the discharge position of HCF by an optical fiber fusion splicer. Then, the tapered air microcavity is discharged multiple times with a small current to improve the reflectivity of the microcavity. RFPI is an open air cavity. A section of HCF and Single-Mode Fiber (SMF) with an inner diameter of 80 μm is directly fused, and the length of the HCF cavity is precisely controlled by a precision cutting platform, so that the FSR of the interference spectrum is consistent with the SFPI. Subsequently, a section of HCF with an inner diameter of 10 μm is splicing on the end face.The parallel structure only consists of SMF and HCF, and the thermal expansion coefficient and thermo-optic coefficient of silica and air are very small, which reduces the crosstalk effect of temperature on tensile force. Through theoretical analysis, it is found that when the optical path difference between SFPI and RFPI is close to when not equal, a Vernier effect can be formed, and the smaller the optical path difference ratio between the two, the greater the sensitivity magnification. In order to form a high-quality Vernier envelope, a fiber attenuator is added between the RFPI and the fiber coupler to adjust the insertion loss of the RFPI to match the energy of the SFPI. The influence of the fiber attenuator on the Vernier envelope quality is verified by numerical analysis and experiments. The experimental results show that after adding the fiber attenuator, the contrast ratio of the Vernier envelope is increased from 0.05 to 0.2, and the magnification is four times.In the experiment, SFPI with a cavity length of 67 μm is prepared for tensile force test. In order to verify the hysteresis of the tensile force sensor, the experiments of increasing and decreasing the tensile force are carried out, respectively, with the sensitivities of 4.022 nm/N and 3.986 nm/N. In order to further increase the tensile force sensitivity of the sensor, two RFPIs with cavity lengths of 80 μm and 63 μm are prepared in this experiment, and formed parallel structure 1 and parallel structure 2 with SFPI, respectively. Tensile force experiments are carried out on two groups of parallel structures. With the increase of tensile force, the reflection spectrum of structure 1 undergoes a clear blue-shift. The corresponding sensitivity is -19.31 nm/N with the linearity of 0.992, which is 4.8 times larger than the sensitivity of a single SFPI. With the increase of tensile force, the reflection spectrum of structure 2 undergoes an obvious red-shift. The corresponding tensile force sensitivity is 63.5 nm/N with the linearity of 0.993, which is 15.8 times larger than the sensitivity of a single SFPI. The simulation analysis shows that when the SFPI cavity length is greater than the RFPI cavity length, with the increase of the tensile force, the drift direction of the envelope is consistent with the drift direction of the single SFPI interference spectrum.To explore the temperature crosstalk of the sensors, the temperature experiment of single SFPI and parallel structure 1 is carried out, and the temperature measurement range is 100°C ~600 °C. The experimental results show that the temperature sensitivity of single SFPI and parallel structure 1 are 3.93 pm/°C and -18.91 pm/°C, respectively, the sensitivity is amplified by about 4.8 times, and the temperature crosstalk is only 9.8×10^-4 N/°C.To verify the stability of the proposed sensor, structure 1 is tested under different tensile force conditions. The experimental results show that the maximum drift of the Vernier envelope at 0.79 N is 0.02 nm, which proves that the sensor has good stability.In this paper, a high-sensitivity fiber-optic tensile force sensor based on the Vernier effect is proposed, which consists of a parallel FPI structure. By matching the energies of SFPI and RFPI through fiber attenuators, the Vernier envelope quality is optimized. The tensile force sensitivity can be improved from 4.022 nm/N to 63.5 nm/N, and the amplification factor is 15.8 with the linearity of 0.993. The simulation results show that the experimental results are basically consistent with the theory. At the same time, the temperature crosstalk of the sensor in the range of 100°C ~600 °C is only 9.8×10^-4 N/°C.