A solid-state high-power 318.6 nm ultraviolet laser system is introduced, which generates a 637.2 nm single-frequency laser by single-pass PPMgO:LN crystal sum-frequency generation of two infrared lasers at 1 560.5 nm and 1 076.9 nm, then generates 2 W narrow-linewidth continuously-tunable 318.6 nm ultraviolet laser by a four-mirror ring cavity second-harmonic generation of 637.2 nm laser. Based on the laser system, closed-loop feedback intensity stabilization of 318.6 nm ultraviolet laser is carried out with acoustic-optic modulator(AOM). The fluctuation of laser intensity in time domain is suppressed from ±11.12% to ±0.08% , and effective bandwidth of feedback loop in frequency domain is about 13 kHz. Trap-loss spectroscopy of cold cesium atoms is demonstrated by combining ultraviolet laser with cesium magneto-optical trap. It is of great importance to obtain a stable, narrow-linewidth, continuously-tunable 318.6 nm ultraviolet laser for the study of interaction between cesium Rydbergatoms.