A quasi-physical zone division (QPZD) large signal model for GaN HEMT operating on pulse-mode was established. A 20 W high-power GaN HEMT with power-bar structure, fabricated by in-house 0.4 um AlGaN/GaN HEMT process, is used for validation. All the measured data are fulfilled by an on-wafer load pull measurement system. The results show that good agreements between simulations and measurements have been achieved on pulse I-V, multi-bias S parameters, and large signal performance. The results of this paper show that the QPZD model works well for high power transistors at pulse excitation condition.