ThePorroprism resonatorlaserhasthecharacteristicsofhighmechanicalstabilityandgoodbeamquality. The Porroprismwilldepolarizetheincidentlightandthe1/4λ waveplatecannotworkeffectively, soitneedstouseanadaptive waveplate for compensation. Based on Jones matrix, the mathematical model of Q-switching of Porro prism resonator is establishedandsolved. TheoptimalcompensationwaveplateunderdifferentazimuthanglesofthePorroprismisanalyzed. The influence of the waveplate tolerance, the refractive index tolerance and the installation tolerance of the azimuth angle ontheextinctionratio arecalculated. Forexample, thePorroprismisplacedhorizontally, thephasetoleranceofthe wave plate is ±0.02 λ, the extinction ratio is greater than 20 dB. When the Porro prism is placed at 45°/135°, there are four corresponding optimal waveplates. The extinction ratio can be greater than 30 dB within the range of 0±4.66°of the Porro prismazimuthangle.TheseresultsprovideabetterandmoreengineeringbasisforthedesignofQ-switchedlaserwithPorro prismresonator.