In the MOPA system, the smooth spatial and temporal shapes and a long coherent length of the output laser pulses are the essential requirement to the master-oscillator. With the development of DPSL, it becomes the first choice of the master- oscillator in the MOPA laser system. In this paper, a single-longitudinal-mode DPSL with short length resonator and end-pumped Nd:YAG using LN Q-switching is presented. Through arranging the optical components in the resonator reasonably, controlling the depth of the focusing point in the Nd:YAG, decreasing the effects of the stationary waves to laser mode, and without using any special selecting-mode component, the single-longitudinal-mode output energies of 50～100 μJ are attained. On the repetition of 40 Hz, the following performance are achieved