A laser radar based on ranging principle of gain modulation is introduced, and its distance measurement accuracy under shot noise limited circumstances is analyzed. According to the accuracy model, a method which uses techniques of image registration and superposition is presented to improve ranging accuracy in airborne applications. For differences of distance accuracy among range image sequences, a weighted processing before registration is used for the purpose of assigning high weights to pixels with high accuracy, and a registration method called up-sampled phase correlation is used to locate image sequences accurately. The range images after registration are weighted superposed to minimize range error. Theoretical analysis shows that this method can effectively integrate detected signals among different frames. If n frames range images are superposed, the range error will be 1/n of one frame. Simulation and experimental results are demonstrated to verify the effectiveness of this method.