To improve the temperature sensitivity and data integrity of the fiber laser, a fiber laser temperature sensing system based on beat frequency demodulation is proposed. The fiber Bragg grating (FBG) in the fiber laser resonator is used for temperature sensing. The wavelength change of FBG is successively transformed into the wavelength change of the resonator and the frequency shift of the fiber laser beat frequency signal, which greatly improves the sensitivity of the system. The Python program is used to realize the second-time data automatic collection and saving, thus improving the working efficiency. The error caused by large frequency jitter can be avoided by demodulating the temperature signal through the rectangular frame center position method instead of direct peak value finding method. Compared with optical demodulation technology, the system uses mature electrical demodulation technology to demodulate instead of expensive wavelength demodulation instrument, reducing the cost of modulation. The experimental results show that the system has high sensitivity and measurement accuracy. The average sensitivity of the system is 74.087 kHz/℃. The measurement accuracy of the system is 0.47×10^-3 ℃.