Abstract: For the 3μm~5μm angle-tuned ZnGeP2optical parametric oscillator,an theoretical design of the ZnGeP2parameters is presented.The angle-tuned curve,effective nonlinear coefficient curve and parametric gain curve are calculated respectively,phase-matching angle of the optical parametric oscillators(OPO) and cut angle of the crystal are determined.The walk-off angle and acceptance angle of the crystal are calculated too,which are of some reference value to the experiment research of the ZnGeP2optical parametric oscillator.