Abstract: For studying the beam stability of high power solid-state lasers,drift error of main beam was analyzed on the basis of shooting error budget of prototype facility.The drift angle of main laser must be less than 10.6μrad.In 37 minutes,144 frames of far-field images were collected.Two kinds of methods,threshold and gravity model,were used in far-field image processing with MATLAB.The drift was calculated separately in x direction and y direction.The drift of x direction was 3.47μrad and y direction was 4.09μrad.Results indicate that requirement of the main laser stability is met and the requirement of practical shooting is also met.