The beam automatic alignment system is used to adjust the beam of high power solid-state laser driver and to make the beam accurately point to target. Algorithm of alignment and flow control are two key techniques on beam automatic alignment. Considering the algorithm on alignment of cavity mirror in technical integration experiment line (TIL),three kinds of algorithms:the largest area of image signal,control of long-short axes and the length of x-y axes control are put forward based on image processing. The experiment on TIL indicates that the length of x-y axes control is propitious to closed-loop control of alignment,and the alignment accuracy is less than 90 μm. After wave-front adjusting,alignment system is used to point the far-field again. Result indicates that the influence of the adaptive optics system which makes the far-field alignment error will be able to eliminate.