In order to achieve all-round angle detection in laser warning with a certain accuracy, we proposed a method of measuring laser direction using geometrical projection. By calculating the shading area when laser projects on the board with given parameters, we got the current ratio from the different quadrants of the measurement, and the direction of the incident laser can be judged by the corresponding relation between projection area ratio and angle using the program for angle detection. For a minimum resolution of angle detection, the limit angles are calculated as (0°,90°), (33°, 21°), (33°,69°), (45°,90°) in Matlab, and the minimum voltage 0.05 V in experiment. The simulation calculation and the experimental data show that the design can achieve the detection requirements of the minimum identification of 1°.