A refractive index and curvature insensitive temperature sensor based on PbS fiber is proposed. It is simple in fabrication just by splicing a section of PbS fiber between two single mode fibers without dislocation. Due to the special refractive index distribution of the PbS fiber core, the light can be stimulated to different modes in the core when it couples into the PbS fiber from the input single mode fiber. Different modes interfere when they couple into the output single mode fiber. The optical path differences between different modes of the PbS fiber change when the ambient temperature changes. Finally, the transmission spectrum of the sensor has a variation. Monitoring the variation of the transmission spectrum can measure the ambient temperature. Through the experiments, it is found that a complete periodic interference spectrum can be obtained when the length of PbS fiber is 4 mm. The sensing performances of temperature, refractive index and curvature of the sensor are tested, respectively. The results show that the temperature sensitivity of the sensor is 55.45 pm/℃, the refractive index sensitivity is only 2.08 nm/RIU and the curvature sensitivity is only -0.29 nm/m-1, in which RIU is refractive index unit. It means that the sensor is insensitive to refractive index and curvature. So the temperature sensor can avoid the impact of the refractive index and the curvature. The sensor has a small structure size, and it can be well used in biochemistry, industrial production and other temperature measurement occasions.