In order to achieve the incoming laser’s accurate position, it is necessary to improve the detected laser’s direction resolution. The InGaAs focal plane array detector with the type of FPA-320x256-C was selected as the core component of the diffraction grating laser warning device. The detection theory of laser wavelength and direction based on diffraction grating was introduced. The drive circuit was designed through the analysis of the detector’s performance and parameters. Under the FPGA’s timing control, the detector’s analog output was sampled by the high-speed AD. The data was cached to FPGA’s extended SRAM, and then transferred to a PC through USB. Labview on a PC collects the raw data for processing and displaying. The imaging experiments were completed with the above method. With the wavelength of 1550 nm and 980 nm laser from different directions the diffraction images were detected. Through analysis the location of the zero order and one order can be determined. According to the grating diffraction theory, the wavelength and the direction of the two-dimensional angle can be calculated. It indicates that the wavelength error is less than 10 nm, and the angle error is less than 1°.