Based on a theoretical model of Q-switched laser with the influences of the driving signal sent to the Pockels cell and the doping concentration of the gain medium taken into account, a method of achieving high energy sub-nanosecond Q-switched lasers is proposed and verified in experiment. When a Nd:YVO4 crystal with a doping concentration of 0.7 at.% is used as a gain medium and a driving signal with the optimal high-level voltage is applied to the Pockels cell, a stable single-transverse-mode electro–optical Q-switched laser with a pulse width of 0.77 ns and a pulse energy of 1.04 mJ operating at the pulse repetition frequency of 1 kHz is achieved. The precise tuning of the pulse width is also demonstrated.