To improve the output laser beam quality of a positive-branch confocal unstable resonator, an auto-alignment and stabilization cavity laser system is presented. The tilt aberration measured by a Hartmann-Shack (H-S) sensor is taken as the feedback parameter, and a step-motor is used to control the concave cavity mirror, and a classic PID algorithm is adopted to compensate for the tilt aberration and stabilize the output laser beam. Theoretical and experimental results proved that this system can correct the tilt aberration in real time and the output laser beam becomes stable when the aberration is moved out.