Abstract: Laser warning system is a type of electro-optic countermeasure equipment, which can detect the wavelength and azimuth of the incident laser. Based on the principle of the grating diffraction, DSP signal acquirement and processing system, a laser warning system was designed and realized, which could detect the wavelength and the azimuth of the incident laser, and send out alarms. The design of hardware and software were studied in the paper, the math model of the grating diffraction was built, the math expression of the calculation of the wavelength and azimuth was deduced, then, the laser system experiment was studied. Experimental results showed that it can detect the laser and send alarms immediately, and measure laser wavelength and incident direction, the range of the wavelength and the incident is 500 -1 100 nm and 13respectively, the maximal error of wavelength is 10 nm, and the maximal error of incident direction is 1.