The invention relates to an intracavity aberration compensating unstable cavity laser device and an aberration compensating method thereof. The intracavity aberration compensating unstable cavity laser device comprises an unstable cavity mirror, a coupling output mirror, a laser gain medium, a pump device, a detection light source, a detection light leading-in mirror, a detection light leading-out mirror, a detection light wavefront detector and at least one compensation element, wherein the detection light wavefront detector detects a led-out detection light beam, corrects an optical path length modulation function of the compensation element based on the led-out detection light beam, and achieves intracavity aberration compensation of an unstable cavity. The intracavity aberration compensating unstable cavity laser device and the aberration compensating method thereof achieve the active optical compensation for the unstable cavity with high intracavity optical distortion, and obtains high-quality laser output; the compensation method has high universality; the intracavity insertion loss is small, the depolarization effect does not exist; the algorithm is simple, and the compensation solving rate is increased; and the overall structure is simple and convenient in debugging and maintenance, the adopted elements are all commercial elements and elements convenient in customized processing, and the practicability is very high.