The invention provides a polarization maintaining optical fiber interferometer capable of simultaneously measuring strain and temperature. The system comprises a narrow-band light source, a total polarization-maintaining Mach-Zehnder interferometer, an interference signal detection unit, a differential circuit and a demodulation system. A polarization-maintaining optical fiber device is adopted toconstruct a full-polarization-maintaining interferometer, and the optical signals are simultaneously transmitted in the fast axis and the slow axis of the polarization maintaining optical fiber, andtwo sensing systems are formed. The two sensing systems have different responses to the temperature and the strain respectively, so that simultaneous measurement of the two can be realized. The Mach-Zehnder interference structure does not have back-reflection transmission, and rayleigh scattering noise in the light transmission process is effectively inhibited. Light in the polarization maintaining optical fiber is separated from the fast and slow axes, the differential circuit is used for carrying out differential processing on the coaxial signals, the noise is reduced, and the measurement precision is improved. The polarization maintaining optical fiber interferometer is simple to manufacture, convenient to measure, high in precision and capable of effectively overcoming the problem of cross sensitivity. The polarization maintaining optical fiber interferometer can be applied to the fields of oil exploration, and seismic observation.