The laser diode (LD) ring uniformly side-pumped laser oscillator has the characteristics of simple structure, high beam quality and large single pulse energy, etc and it is often used as the oscillator stage of main oscillation power amplification (MOPA) structure of the oscillator in high-energy pulsed solid-state lasers, which is an important direction of the domestic and foreign researchers' research. In this paper, the influence of different arrangement of laser diodes and different absorption coefficients of working materials on the absorbed light field is simulated by Zemax software. Based on the simulation results, a ring side-pumped structure with 20 bar strips in series is designed to improve the uniformity of crystal absorption. Through the ring side-pumped structure, with the unstable resonator design, a laser oscillator is built for experimental study. A 1064 nm laser with a single pulse energy of 496mJ and a pulse width of 12.4 ns is achieved at a repetition rate of 100 Hz, with a beam quality better than 9mm·mrad and an optical-optical conversion efficiency of 18.5%. Moreover, the oscillator can maintain the stability of optical axis at the same time, to realize 20 ns pulse width the within variable gear adjustable. The experimental results show that the ring side-pumped structure is reliable and effective, which provides an effective scheme for selecting the oscillation stage of MOPA structure.