Composite YAG/15 at. % Yb:LuAG/YAG transparent ceramic planar waveguide was fabricated by a tape casting method and vacuum sintering technology. Under a 970 nm diode laser pumping, the absorbed efficiency of 85.4% was achieved, and efficient CW laser operation at 1030.7 nm was accomplished with a good beam quality with Gaussian spatial profile. A maximum output power of 288 mW was obtained under a pump power of 4.69 W, corresponding to a slope efficiency of 9% and an O-O conversion efficiency of 5%.