Recent studies have revealed that space beam interferenced in the gain medium would result in space burning hole phenomenon and form the gain grating. The gain grating formed by the four-wave mixing function after multiple oscillations in the resonator has self-adaptive, self-Q-switched and spatial filtering capabilities, and can obtain holographic conjugate output. Based on the above characteristics of the gain gratings in a non-reciprocal laser cavity with a grazing incidence structure, we analyze the factors which affect the output single-frequency stability and output energy with diode-pumped monolithic Nd∶YVO4 crystal, and achieve a single-longitudinal-mode Q-switched output with a single pulse energy of 0.9 mJ, a pulse width of 7.5 ns, and a line width of 0.95 pm by optimizing the extinction ratio of the non-reciprocal element, the gain area, the size of self-intersecting angle and other conditions. As far as reviewed, this is the maximum energy achieved by the current monolithic gain media, which can provide references for analyzing and optimizing the single-longitudinal mode oscillations to achieve stable non-reciprocal gain grating lasers.