The laser beams automatic alignment system is used to adjust beam lines automatically in the high power laser fa2cility for inertial confinement fusion. Image processing is one of the key techniques in laser beam automatic alignment. Consider2ing the SG-Ⅲ, combining different kinds of methods in image processing such as threshold, gravity model, median filter, cir2cle fitting and so on, a reasonable scheme for automatic alignment was presented. It was demonstrated on the simulation experi2ment system. Results indicated that beam paths adjustment can be finished in 15 minutes by the automatic alignment system.The precision of the near field adjustment was less than 0.5 % of the spot. The accuracy of the far field adjustment was lessthan 0.3″. Requirements of the SG-Ⅲprototype facility are met.