In this paper, a high-power and high-efficient 4.3 µm mid-infrared (MIR) optical parametric oscillator (OPO) based on ZnGeP2 (ZGP) crystal is demonstrated. An acousto-optically (AO) Q-switched Ho:YAG laser operating at 2.1 µm with a maximum average output power of 35 W and pulse width of 38 ns at a repetition rate of 15 kHz is established and employed as the pump source. A doubly-resonant OPO (DRO) is designed and realized with the total MIR output power of 13.27 W, including the signal and idler output power of 2.65 W@4.07 µm and 10.62 W @4.3 µm. The corresponding total optical-to-optical and slope efficiency are 37.9% and 67.1%, respectively. The shortest pulse width, the beam quality factor and the output power instability are measured to be 36 ns, Mx2=1.8, My2=2.0 and RMS<1.9%@8 hours, respectively. Our results pave a way for designing high-power and high-efficient 4-5 µm MIR laser sources.