Based on dual-wavlength action and sum-frequency-mixing theory,a series of optical thin film for LD pumped Nd∶YAG crystal,LBO intracavity sum-frequency-mixing 500.8 nm laser are designed and manufactured. To obtain optimum output power,the coating design of resonator mirror is analysized. The method that adjusts one resonator facet reflectivity for fundament laser by fixing the other resonator facet reflectivity is used,by computer thin film optimization methods based on the reasonable starting desing.The dielectric high reflective laser mirror for 500.8 nm laser is achieved by double ion beam sputter technique,which is controlled by a time-power monitoring method. An optimized CW 500.8 nm laser at room temperature is obtained for the first time in China. The maximum laser output power of 20 mW is obtained when a incident pump laser of 1.8 W is used.