Abstract: GaN-based high electron mobility transistor (HEMT) has received much attention for its excellent performance in high-frequency, high-power, and high-temperature applications. Metal-insulating-semiconductor high electron mobility transistor(MIS-HEMT) improve device performance by introducing an gate insulating layer, especially reducing gate leakage current and increasing breakdown voltage. However, MIS-HEMT using recessed-gate structure presents challenges in achieving threshold voltage (V_th) uniformity. An enhancement-mode recessed-gate structure AlGaN/GaN MIS-HEMT device with triple barrier layer is numerically investigated using Silvaco TCAD software. Compared to traditional Schottky gate HEMTs, the three barrier layer enhancement-mode AlGaN/GaN MIS-HEMT uses piezoelectric neutralization technology (PNT) to achieve high V_th uniformity. In order to obtain better direct current characteristics of the device, the effect of changing the Al component of buffer layer and PNT layer on the device is studied. In addition, the dependence of device size scaling (such as gate drain distance L_gd and gate length L_g) on direct current characteristics is analyzed in detail. The optimized MIS-HEMT has a V_th of 0.8 V, an output current of 0.43 A/mm, and a saturation leakage current of 1.99 A/mm. The maximum transconductance (g_mmax) is 0.14 S/mm, and the specific on-resistance (R_on,sp) is 1.64 mΩ·cm². The results of this study have important guiding significance for the design and optimization of AlGaN/GaN MIS-HEMT structures with three barrier layers.rier layers.