Multi-pass amplifier technology becomes the main development direction of high power solid-state laser driver, it is necessary to debug and maintain the laser optical path and establish the mathematical model and adjustment scheme of the beam alignment. Using matrix optics method, a multi-pass amplifying automatic collimation system mathematical model is set up, the far and near field laser facula offset is obtained with the analytical expression of the adjustment quantity. The feasibility of light path principle and adjustment method of automatic collimation system is validated.