In view of the output signal from the capacitive grating sensor easy to be influenced by the instantaneous speed of the drive shaft during rotating shaft power test, a rotating speed calibrating device based on field programmable gate array (FPGA) is proposed. Based on the high precision photoelectrical encoder, the D-flip flop is combined with the 4~16 decoder of HCC4515B to filter peak burr output from the photoelectrical encoder. And the detailed circuit implementation scheme taking FPGA as the main control unit is given. Test results show that the rotating speed calibration device can achieve the desired effect.