Frequency modulated continuous wave(FMCW)laser modulation circuit is an important part of the FMCW laser detection system. In this paper, the method of FMCW laser modulation was studied and a laser modulation circuit composed of a linear frequency modulation signal producing circuit and a semiconductor laser driver circuit was designed and implemented. Experimental result is given. The linear frequency modulation signal producing circuit was designed using the direct digital synthesis chip AD9958 and produced a 10-110 MHz sawtooth linear frequency modulation signal. The semiconductor laser driver circuit modulates the laser intensity with the linear frequency modulation signal through direct current modulation. Test results show that the laser modulation circuit can meet the design requirements：frequency deviation of 100 MHz, frequency modulation period of 100 μs.