Abstract: A coherent demodulated circuit has been designed to control a spectrum generated by a frequency stabilized femtosecond laser. In the circuit, the frequency repetition rate which was about 90 MHz and the offset frequency which was about 10 MHz by using only one photoelectric receiver were obtained. SNR of the output signal reached 20 dB in the experiment. This result provided a convenient and significant method for farther control of a femtosecond laser.