The energy level structure of the Cr,Er:YAG crystal is studied, the energy resonance transfer pro. cess from the Cr3+ to Er3+ , and the energy level transition process of the 3 μm laser are also discussed. The xenon lamp pump source and the Cr,Er:YAG laser are designed and constructed at room temperature. The relationships be.tween the output energy and the pump energy, the output energy and the crystal temperature are analyzed. In the sin. gle-shot free running operation, the maximum output energy, the pulse width and the slope efficiency are 529 mJ, 103 μs and 0.26%, respectively. The spectrum range is 2 923 nm to 2 940 nm, and the two peak wavelengths are 2 930 nm and 2 933 nm respectively. Experimental results show that the Cr, Er:YAG crystal is an efficient candi. date for the 3 μm laser operation.