This study proposes a microwave heating energy supplement technology for gas hydrate reservoir. The microwave radiation simulation model of the leaky coaxial antenna is established by HFSS. Based on the simulation results of microwave antenna structure parameters on the radiation performance, the optimized shape, angle, length, width and fillet of the slot are rectangle, 80°, 38 mm, 12 mm and 2 mm, respectively. To compare the heating performance of microwave antenna before and after optimization, a microwave heating simulation model for hydrate reservoir is developed, which is validated by experimental results. The comparison results illustrate that, after microwave heating 10 h with the optimized antenna structure, the average temperature within a 1-m radius of natural gas hydrate reservoir increases to 10.613 °C, which is about 5.5 °C higher than that before the optimization. The aforementioned results suggest that the optimized microwave antenna structure significantly increases the temperature of the hydrate reservoir, providing the necessary energy to drive hydrate decomposition. The proposed microwave energy supplementation technique holds promise for advancing the efficient development of natural gas hydrates, the further investigation of effect of which on gas production within hydrate reservoirs is needed for future application.