In order to minimize the dispersal of Photon Spectrometer(PHOS) channel gains, we have to adjust the bias voltage of APD so as to compensate the following factors: wide dispersal of the APDs gain factors, gain dispersal of the preamplifiers and light yield dispersal of the PWO crystals. So, we designed the circuit for APD bias control based on FPGA This circuit control the 10-bit DAC via FPGA to make the range of bias voltage achieved 210V-400V, the adjust precision of the range of bias voltage a-chieved 0.2V/bit This paper introduced the APD b...