An average power of 138 W green beam operation by intracavity frequency doubling of acousto-optic Q-switch solid-state Nd∶YAG laser is reported. An U type resonator is designed and optimized in order to compress pulse-width and increase the average power. Two Nd∶YAG rods were employed and a type Ⅱ phase matched KTP crystal (=25°, θ=90° under the condition of 24 ℃, the size is 7 mm×7 mm×7 mm) was applied for frequency doubling. Under the pumping currents of 18.5 A and 20.5 A, a maximum green power of 138 W was generated at 10 kHz repetition rate and 49 ns pulse-width, leading to 14.1% of optical-optical conversion efficiency and ±2.8% instability.