In order to develop a single-frequency pumping source for an optical parametric oscillator, a seed-injected, single-end pumped, Q-switched, bonded Nd∶YAG single-frequency laser with 500Hz pulse repetition rate was designed by using the ramp-fire resonance detection technique with bias feedback, and a single longitudinal mode oscillation was established. The technology was analyzed theoretically. The results show that, when pump energy is 36.8mJ, output single pulse energy is 8.4mJ and optical efficiency is 23%, pulse width is 6.8ns, beam quality factor M2 is about 1.3, and peak power is 1.2MW. The interference pattern of output laser is obtained by using a F-P etalon. After one hour observation, single longitudinal mode probability of laser output is 100%. The result is helpful for the pump design of optical parametric oscillators.