The methods of producing mid-infrared laser are introduced, and the latest progress of the mid-infrared laser output obtained by optical parametric oscillation technology at home and abroad is expounded importantly. The technical characteristics and problems of the optical parametric oscillator (OPO) based on nonlinear crystals, including ZnGeP2(ZGP), KTiOAsO4(KTA) and periodically poled LiNbO3(PPLN), are analyzed. The developing tendency of the mid-infrared laser produced by optical parametric oscillator technology is discussed.