Characteristics of Er level structure and laser rate equation of an Er3+:YAG four-level system are analyzed. In the laser system, dual-lamp laser, double-elliptical cavity and spike pulse discharge are used to increase pump rate. Through increasing reflectivity of laser cavity and decreasing laser threshold Er3+:YAG laser can output 2.94 μm high-repetition-rate spike pulse laser. In order to eliminate the influence of heat effect, high-tension and high-speed laminar flow cooling technology is adopted. 2.94 μm Er3+:YAG laser with repetition rate of 40 Hz and single pulse energy of 0.5 J is achieved.