This article improves the mobility part of the ASM GaN model, and provides the corresponding multi-temperature DC parameter extraction process based on the existing ASM GaN model, in order to address the accuracy of the ASM GaN model at different working environment temperatures in AlGaN/GaN HEMT Devices. In addition, this article validates the accuracy of the improved ASM model through parameter fitting. Compared with previous models, the modified model has higher accuracy and fewer temperature parameter values in the parameter extraction process at multiple temperatures.