Abstract: In order to obtain the relative position of ground target in real time for semi-active laser terminal correction projectile before trajectory correction, a localization algorithm to acquire the target relative position was proposed which using measurement information from onboard laser detector and projectile's attitude, trajectory height obtained from previous ballistic information. Target localization model was established, with the Monte-Carlo simulation, the impact on localization precision from the look angle error, the projectile's attitude error and trajectory height error was analyzed in different quadrant elevation angles respectively. The results indicate that, the maximum influence factor on the localization precision is the trajectory height, but the largest localization error is less than 12 m caused by the single error factor; the localization precision increases with the increasing of quadrant elevation angle. The proposed target localization algorithm meets the accuracy and real-time requirements.