The time-varying fiber optic grating sensing signal is usually affected by noise, environmental interference, etc. In order to improve signal quality, a precise subdivision method for time-varying fiber optic grating sensing signal under FPGA technology is proposed. Analyze the principle of fiber optic grating displacement measurement and the causes of moire fringes, and use them as the basis for moire signal subdivision; By combining hardware and software subdivision methods using FPGA technology, a time-varying fiber Bragg grating sensing signal subdivision circuit is designed. Based on the subdivision circuit, a spatiotemporal conversion subdivision method is introduced to perform signal subdivision processing, in order to improve signal subdivision accuracy. The experimental results show that the proposed method has a maximum subdivision error of only 0.58 mm at different subdivision multiples, and a minimum subdivision error of only 0.19 mm in noisy environments, indicating that the method can achieve high-precision subdivision of time-varying fiber optic grating sensing signals.