Incident laser passing through sinusoidal grating diffracts as zero-order and plus or minus one-order spectra. The wavelength and direction of incident laser can be measured by reading the position of the spectrum from the detector. In order to detect the wavelength and direction of laser light, a staring laser detecting and warning system based on sinusoidal grating is designed. Working principle of the system is introduced, computing formulas of wavelength and azimuth of the incident laser are deduced, and detecting accuracy is studied by numerical simulation. Influence of grating constant and cylindrical lens radius on detectivity of the system is studied and the related function is provided. Experimental results show that the laser detecting and warning system can realize real time measurement of laser with the wavelength range of 320~1100 nm, field of view of ±20° when the grating constant is 1/500 nm and the cylindrical lens radius is 20 mm, where the wavelength resolution is less than 10 nm and the angular resolution is less than 1°.