The utility model discloses a box -type substation air cycle dehumidification system that cools down, include: automatic control dehydrating unit, a temperature sensor, the 2nd temperature sensor andfan, automatic control dehydrating unit includes controller and dehumidifier, the dehumidifier is connected with the controller, and a controller and a temperature sensor, the 2nd temperature sensor and fan link to each other respectively, the fan sets up on the box -type substation casing for when a temperature sensor determine's ambient temperature and the 2nd temperature sensor determine's ambient temperature's difference is greater than predetermined temperature difference value, with the outer air suction dehumidifier air inlet of box -type substation, and with the air mixing that dehumidifies that waits of dehumidifier air inlet department. Additionally, the utility model also discloses a dehydrating unit. Adopt the utility model discloses, save the energy, improved the efficiency ofdehumidification.