Abstract: The SiC MESFETs nonlinear characteristic is modeled by modified Triquint's own model (TOM) DC I-V model and Angelov nonlinear capacitor models. The nonlinear model has been implemented in Agilent advanced design system (ADS) by using symbolic defined devices (SDD), and an integral SiC MESFET process line design kit has been embedding in ADS. Its validity is verified by measured DC I-V curves, multi-bias S parameters and harmonic balance simulation based on native SiC MESFET process line, and good accuracy has been achieved.