Abstract: The frequency-offset-lock control system which is applied to the heterodyne signal of narrow pulse laser is designed based on the programmable logic device since the frequency-offset-lock technology is widely used in laser heterodyne detection and laser radar. In the design, ultrahigh-speed comparator was applied for the waveform conversion, the multi-pulse frequency discrimination and maximum probability median filtering were adopted for the digital frequency discrimination, the fast control by small step was used for the frequency modulation, and the D/A convertor and linear magnification circuit were used to output the frequency modulated signal. The simulated heterodyne signals with the 40ns pulse width generated by the signal generator were employed to simulate the whole system, and the design function was realized. The simulation experiments show that the error range of the frequency discrimination gained by the designed frequency discriminator and modulator is -7.5MHz～+7.7MHz when the pulse width is 40ns.