To scale the output power of all- solid- state continuous- wave Nd∶GdVO₄ laser of single- frequency operation at 1342 nm, the composite Nd∶GdVO₄ laser crystal is used as laser medium, and its relevant parameter is optimized. The theoretical calculation shows that the thermally induced diffraction losses is proportional to the cross- section dimension of laser medium, and the pump power of thermal fracture limit is the decreasing function of it. A ring laser resonator is designed to make the laser single-frequency operation. The experimental result shows that the maximum output power is 3.1 W, and the conversion efficiency increases by 30%.