Gas explosion seriously threaten the employees security and restrict the safe production of coal mines. Therefore, it is particularly essential to investigate the prevention and control of gas explosions. In this study, a two-dimensional numerical model of a spherical explosion tank was developed to explore the effects of water vapor on gas explosions in a high-pressure environment. Explosion parameters of 10% gas, 1 MPa pressure, and water vapor contents varying from 0% to 8% were simulated using FLUENT software. The results show that the maximum explosion pressure and temperature of the premixed gas gradually decrease with increasing water vapor content, i.e., when the water vapor content is increased from 0% to 8%, the maximum explosion pressure and temperature of the gas mixture decreases from 2.52 MPa and 2092 K under dry conditions to 1.62 MPa and 1714 K with 8% water vapor. The attenuation amplitude is also reduced upon the addition of steam. Water vapor in premixed gas therefore plays a vital role in suppressing gas explosions.