The　optical　permitted　parameters　and　angle　tuning　characteristics　of　ZnGeP2　(ZGP)-OPO　were　numerically　simulated　based　on　the　dispersion　equation　of　ZGP　and　the　momentum　and　energy　conservation　in　type-I　and　type-II.　The　angle　tuning　ranges　of　50.7-57　in　accordance　with　wavelength　tuning　from　2.4　μm　to　11　μm　in　type-I,　and　the　wavelength　tuning　ranges　of　2.4-11.5　μm　(in-continuity　3-6　μm)　with　angle　tuning　58-87　in　type-II　have　researched.　The　acceptance　angle　and　walk-off　angle　in　the　process　of　angle　tuning　were　also　numerically　simulated.　Furthermore,　the　permitted　parameters　of　ZGP　were　compared　with　AGS　and　AGSe　crystal.　The　conclusions　showed　that　ZGP　is　the　optimum　mid-infrared　crystal.