Abstract: In order to accurately simulate the microwave noise performance of Gallium Nitride high electron mobility transistor (GaN HEMT) at low temperature, a method for constructing a low-temperature noise model based on small signal equivalent circuits is proposed. Based on the frequency dependence of the admittance parameters to obtain the equivalent circuit components of the small signal, an accurate small signal model is established, and on this basis, the low-temperature noise sources are characterized according to the Pospieszalski principle, especially the shot noise introduced by gate leakage, and the low-temperature noise model is established. The simulation results show that the maximum error of the S-parameter of the small-signal model is 2.5% in the frequency band of 0.2−40 GHz, and the maximum error of the four-noise parameter of the noise model in the frequency band of 2−10 GHz is only within 1%. Among them, the gate leakage shot noise contribution is about 0.1 K at low temperature, which has a certain effectiveness and accuracy compared with the traditional method.