Based on GaAs planar Schottky diode process, a W band wideband frequency tripler MMIC is designed with a reverse parallel diode pair in this paper. By combining of finite element method and equivalent circuit method, an accurate equivalent circuit model of the planar Schottky diode is built in the frequency range of 10~280GHz. The nonlinear harmonic balance tool is utilized to achieve the optimal frequency tripler design in W band. The measurement results show that the frequency multiplication loss is less than 15dB under 17dBm driving power, efficiency up to 6.7%. The chip size is 0.80mm×0.65mm×0.05mm．