Based on the analysis of short-channel effects and device modeling of Nano-gate AlGaN/GaN high-electron mobility transistors (HEMTs), the key device characteristics of gate-length from 500 down to 50nm have been studied by numerical simulations. And the relationship between aspect ratio (the ratio of gate-length and the thickness of barrier layer) and the degeneration of these parameters is discussed in detail. The results show that the simulated electrical characteristics are in good agreement with reported experimental data.