In order to improve the imaging speed of full-field optical coherence tomography for practical applications, a phase modulation method for rapid full-field optical coherence tomography was proposed. The Field－Programmable GateArray (FPGA) was used to build the circuits to generate accurate sinusoidal and pulse signals with adjustable frequency. The generated signals were then employed as modulation signals in four step phase shift method to obtain optical sectional images. Finally，the optical tomography images of onion cells were obtained and compared with the ones generated by traditional phase shift method and the single chip-based method. The results show that the method proposed not only can improve the image quality, but also can increase the imaging speed, the time required for reconstructing an optical tomographic image is reduced from 4 s（0.25 Hz） to 0.03～0.05 s（20 Hz～35 Hz）.