A stable all-solid-state single-longitudinal-mode acoustic-optic Q switched laser was developed based on a Nd:YVO4 crystal quasi-continuously pumped by an 880 nm laser diode and unidirectional travelling wave laser operation achieved by a 6-mirror ring cavity . The stable single-longitudinal-mode pulsed laser operation was realized by inserting an acoustic-optic Q-switch and combined etalons in the cavity. With the optimization to the transmissivity of the output coupler, laser pulse width can be narrowed and the single pulse energy can be increased. Laser output with repetition rate of 1 kHz, pulse width of 23.5 ns and single pulse energy of 1.64 mJ was achieved at the peak pump power of 29.1 W. This single pulse energy possesses a long-term stability better than ±1.3% within 2.5 h.