Abstract: To improve the performance of chemical oxygen-iodine laser(COIL) beam, a three-point dynamic collimation method is proposed, and a resonator auto-alignment system with auto-adjusting function is designed. The system uses position sensitive device(PSD) as the position detecting element, three groups of PZT as the driving element. The coupling model of the system is presented. Multivariable self-adaptation closed-loop decoupling arithmetic is used to design a three-input-three-output decoupling controller, resulting in high precision dynamic alignment and high qualily light beam. Experiments indicate that the collimating range of the system is 4 mrad, the precision is 5 mrad and the frequency response is 20 Hz, which meet the demand of resonator alignment system for COILs.