The transmission of the output coupler is analyzied and calculated when the Nd∶YAGis operating in dual-wavelength simultaneously. It is proposed that decreasing the transmission of the output coupler at the wavelength with lager gain properly contributes to the increasing of the output power of the intracavity sum-frenquency mixing . A dual-wavelength continous wave(CW) diode-end-pumped Nd∶YAGlaser that operates at 1064nm and 1319nm simultaneously is demonstrated.By using of the intracvity sum-frequency mixing in type Ⅰcritical phase-matching LBO crystal and optimizing the transmission of the output coupler ,the maxium output power of the 589nm yellow laser is 20mW.