The optical absorption at 9 μm to 10 μm related to lattice vibration in ZnGeP2 crystal limited its application in the mid- and far-infrared range. To explain the physical mechanism of the infrared cut-off edge and the absorption peak near 9 μm in ZnGeP2, a method combining theoretical calculations and experiments was used. Thus, the ZnGeP2 single crystal was grown by the Bridgman method, and the temperature-dominated and pressure-dominated Raman spectrum of the grown ZnGeP2 crystal were tested. In addition, the vibration frequency of ZnGeP2 in the center of the Brillouin zone, the crystal lattice constant and Raman shift peak under different pressures were calculated based on the first-principles method. Experimental and theoretically calculated results reveal that the frequency of the vibration red shifts with temperature increasing, simultaneously, decrease of intensity and wider half-peak width of the vibration are observed. Besides, the frequency of the vibration blue shifts with pressure increasing, simulatenously, decreases of intensity and wider half-peak width of the vibration are observed.