High repetition rate and large energy passively Q-switched Nd:YAG laser side-pumped by continous-wave (CW) laser diode is reported by using Cr4+YAG crystal as saturable absorbers. Regarding operation material as thermal thick lens, the laser beam parameters of plane-plane cavity, plano-concave cavity and plano-convex cavity are calculated according to the ABCD matrix theory of resonators. By comparing the fundamental mode volume, plano-convex cavity is selected. A high repetition rate and large energy passively Q-switched laser beam is obtained, and the TEM00 mode is achieved. A single pulse energy of 2.46 mJ, peak power of 24.36 kW, repetition rate of 4.22 kHz, pulse width of 101 ns are obtained at a pump power of 136.20 W, the amplitude fluctuation and frequency fluctuation are about 5%, the corresponding M2 factor is about 1.3, and the beam divergence angle of far-field is less than 1.5 mrad.