The underground powder magazine wall temperature was lower than the air dew point temperature, caused wall condensation, a large number of water precipitation came out, which made the powder magazine in a humid and foggy environment, had a great influence fire products and staff's physical and mental health. In order to solve this problem, Xingtai Mine successfully developed mining flameproof isothermal dehumidification system, realized the isothermal dehumidification, powder magazine without condensation phenomenon, which reached the expected goal.