In order to realize the design of temperature sensor with lower cost, a new type of intensity modulated optical fiber temperature sensor is proposed. It mainly consists of light source with band-width spectrum, 3-port circulator, fiber coupler, polarization controller, polarization maintaining fiber (PMF), photodetector and signal processing unit. Under the condition of short PMF fiber, the temperature change will have a direct impact on the birefringence of PMF fiber, resulting in a certain phase shift change of the two coherent beams, thus they will have different transmission spectra after Sagnac interferometer, that is, wavelength drift occurs. By using photoelectric conversion and signal processing, the detected light signal is converted into a voltage signal, which is solved to complete the temperature detection. Therefore, without the need for a spectrum analyzer, the measured temperature can be calculated according to the temperature-dependent change function by measuring the transmission spectrum of the Sagnac interferometer. Experiments were carried out in the temperature range of 25~50℃. The test results show that the sensitivity of the optical fiber temperature sensor is 0.066mW/℃, and the resolution is 0.34℃. It has good application value for constructing temperature monitoring optical fiber sensor network.