A high-repetition-rate electro-optic Q-switched single longitudinal mode laser has been developed. Using a fast electronic circuit negative feedback control system, the laser cavity generates dissipation varying with laser intensity and the quasi-continuous prelase is established, then the Q-switch is turned on based on this prelase. Stable single longitudinal mode laser output is generated with the mode selection of the resonant reflector. The laser has produced pulse with width of 15 ns, maximum pulse energy of 2 mJ at 1 kHz repetition rate, and single longitudinal mode probability of 100% within 30 min. The laser system is compact, simple, reliable and has been used as a master oscillator of master oscillator power-amplifier (MOPA) systems.