Terahertz biomedicine is a hot spot in the field of spectroscopy. The main difficulty lies in how to effectively avoid the interference of moisture and perform sensitive analysis and detection of samples in the liquid environment. Metamaterials terahertz sensors have become an important research method in the field of terahertz biomedical sensing due to their advantages such as high sensitivity, fast detection, and trace analysis. A terahertz liquid-phase sensor chip based on a single-open resonance ring metamaterial was designed and developed. In order to effectively solve the strong absorption of terahertz waves by water, a microfluidic channel with a depth of 50 μm was etched by photolithography. The sensor chip integrates a metamaterial substrate and a PDMS flow channel. In the THz frequency band, there are two resonance peaks located at 0.771 and 2.129 THz. Compared with the THz time-domain spectrum of the blank sensor itself, the addition of liquid caused the phase delay and amplitude of the time-domain peak to decrease. At the same time, because the refractive index of water is greater than that of ethanol, the results of the THz transmission spectrum show that the frequency shift of water is greater than ethanol and peak 2 lagers than peak 1. The above results show that the constructed metamaterial liquid-phase sensing chip is a sensitive refractive index sensor, and it also proves the feasibility of the sensor in measuring liquid samples. In addition, using this chip to study PBS solutions of different concentrations, it was found that the addition of ions in the aqueous solution will cause the red shift of the resonance frequency (using water as a reference). As the ion concentration increases, the amount of change in the resonance frequency will increase in turn, with the largest red shift of 10× PBS, Peak 1 is 22.9 GHz, and peak 2 is 30.5 GHz. Comparing the sensing performance of the two resonance peaks, peak 2 has better sensing capabilities, but Peak 1 is more sensitive to low-concentration ion solutions. Therefore, as a sensitive refractive index sensor, the constructed microfluidic sensor and detection system can develop a sensitive label-free THz sensing platform to provide new ideas for terahertz biomedical research.