A diode sidepumped Qswitched Nd:YAG doubleslab oscillator designed for high power solid state laser has been demonstrated. Diode laser power was transferred by a trapezoidal waveguide plate into the slabs and the optical coupler efficiency was 90%. The oscillator was a convexconcave resonator. Highreflection mirror of curvature radius was 3.0m. A VRM of supergaussian was used for output couplers with curvature radius of 3.0m. The output is of single pulse energy 18.23mJ, pulse width 15.25ns and 100Hz repetition rates and beam quality factor. The output beam was a flat topped supergaussian beam.