A simultaneous measurement system of temperature and strain is proposed and fabricated, which has advantages of low cost and easy structure. The system is formed by combining a long period fiber grating with a polarization-maintaining fiber Sagnac loop. The transmission spectrum of the fiber Sagnac interferometer is modulated by LPFG. The simultaneous measurement of temperature and strain can be realized. The experimental results show that the wavelength of the dip is varied with temperature changing and applied strain on polarization-maintaining fiber, and the intensity of the dip is changed with applied strain on LPFG. The temperature sensitivity of the system is 0.181 81 nm·℃-1, the strain sensitivity of LPFG is 0.005 283 dB·με-1, and the strain sensitivity of polarization-maintaining fiber Sagnac loop is 0.015 72 nm·με-1. The experimental system indicates that the proposal is feasible and has an application prospect.