The effect of intracavity aberrated perturbation on output mode structure properties of passive confocal unstable resonator is been experimentally researched by adopting H-S wavefront sensor and Zernike modal wavefront reconstruction on the basis of numerical simulation. Results show that intracavity tilted perturbation notablely affects outcoupled intensity distribution, and will also increase some high-order aberrations of beam phase properties. However, low-order Zernike tilt aberration is the main component when phase-tilted perturbation is introduced into the resonator. Defocus, astigmatism and coma aberration will all be brought, and also such high-order aberration included in wavefront will directly degrade output beam quality. When correction device of adaptive optics adopted for intracavity aberration correction, correction of tilted aberration should be considered firstly.