In this study, we propose an improved measurement method based on light-curtain sensor, and it can obtain the hitting coordinates of supersonic projectile in a larger dispersion area. First, we analyze the speed properties of the shock wave in an effective detection area (also called light curtain in our field), and then find their change rules related to several key factors, including flight speed of the projectile, its attitude, shape, and the temperature in the testing environment. Next we improve a measurement system using wide-angle light-curtain sensor combined with calibration device of the shock speed; especially, this device with three parallel laser beams can effectively measure the shock speed in the light curtain. According to the related structural relation, we derive several computational formulas combined with the shock speed to obtain the hitting position of the measured projectile. Through live ammunition experiments, the results show that the proposed method is feasible and reliable for the supersonic projectile. Besides high accuracy, it also has many advantages, such as fewer sensors, lower requirement for installation, and larger detection area, by comparison with previous measurement systems.