In beams automatic alignment system，by adjusting the angles of many cavity mirrors and reflectors of laser equipment，the direction and position of beam can meet to the physical criterions. To increase the collimation efficiency of far and near field and reduce the adjustment times for motor，this study proposed a collimation arithmetic. Adjustment arithmetic of round image was implemented in the collimation of cavity mirror. In the collimation of reflector，correlative coefficient matrix was improved from traditional two dimensions to four. By the alignment experiment platform，the arithmetic was proved to be converged rapidly. The adjustment steps of motor were more accurate，and the times of move were less than three，which could meet the collimation precision requirement.