The invention discloses an ultra-wideband gallium nitride device small-signal model and a parameter extracting method thereof. Three interconnected capacitor and cascaded inductor network structure forms are adopted for the grating end, the source end and the drain end of the small-signal model respectively, and the small-signal model comprises 18 parasitic parameters and 10 intrinsic parameters; the parasitic parameters comprise outer layer parasitic capacitance Cpgi1, Cpdi1, Cgdi1 and others, parasitic inductance Lgi1, Ldi1, Lsi1 and others and parasitic resistance Rg, Rd and Rs; the intrinsic parameters comprise intrinsic capacitance Cgd, Cgs and Cds and intrinsic resistance Rgs, Rgd and Rds, wherein an intrinsic current source Ids is equal to Gm plus ta as parameters in ViGme-j omega ta. The model can accurately describe the characteristics of a high-frequency device, has wider application frequency band and can adapt to a W frequency band as the highest; by the utilization of the parameter extracting method, the model parameters can have good stability within the frequency range of 0.2-110 GHz.