In order to obtain a high breakdown voltage and high threshold voltage enhancement-mode GaN device, a P-doped GaN (P-GaN) gate combined with recessed-gate AlGaN/GaN/AlGaN double heterojunction device was proposed. The threshold voltage of the device was up to 3.4 V, and the breakdown voltage was up to 738 V. Using Sentaurus TCAD for simulation, the threshold voltage and breakdown voltage of the traditional P-GaN gate and the P-GaN gate with recessed-gate AlGaN/GaN/AlGaN double heletrojunction device were compared. The results showed that, when the recessed-gate depth was changing at 5~13 nm, the threshold voltage increased with the recessed-gate depth, and the breakdown voltage first increased and then decreased slightly with the recessed-gate depth. The on resistance increased with the recessed-gate depth, and the minimum on resistance was 11.3 Ω·mm.