The invention discloses an efficient intermediate infrared laser crystal Er, Pr: YSAG as well as a preparation method thereof and a method for realizing intermediate infrared laser output. The methodtakes a scandium-contained garnet crystal material yttrium aluminium scandium garnet single crystal with high symmetry as a substrate, Er<3+> is taken as an active ion, and Pr<3+> ion is doped into the crystal, so that particle number of energy level <4>I<13/2> under laser at a wave band of 2.6-3.0 mum of Er<3+> ion is effectively evacuated, fluorescent lifetime of the energy level is shortened, alaser threshold value is reduced, laser output efficiency and laser output power are improved. A semiconductor laser unit is adopted for pumping crystal, so that laser output at a wave band of 2.6-3.0 mum is realized, and important application prospect in the fields such as laser medicine, scientific research and military science is realized. At present, an InGaAs LD laser unit is adopted as a pumping source for pumping Er, Pr:YSAG crystal, so that double-wave-length intermediate infrared laser output with wavelength being 2.694 mum and 2.825 mum is realized.