The invention relates to a substation intelligent frequency conversion combined dehumidification system and a dehumidification method. The dehumidification system comprises a centralized dehumidification unit, a separate online regeneration dehumidification unit and a control unit. The control unit is connected with the centralized dehumidification unit and the separate online regeneration dehumidification unit. The centralized dehumidification unit comprises a frequency conversion dehumidifier, a first dry wind supply header pipe which provides dry wind for an underground cable trench and a switch cabinet, a second dry wind supply header pipe which provides dry wind for a centralized outdoor terminal box, a first dehumidification header pipe which is used for pumping wet air from the underground cable trench and the switch cabinet, and a second dehumidification header pipe which is used for pumping wet air from the centralized outdoor terminal box. The separate online regeneration dehumidification unit comprises an online regeneration dehumidifier, a fourth dry wind supply branch pipe which is used for providing dry air for a remote independent terminal box, and a fourth dehumidification branch pipe which is used for pumping wet air from the remote independent terminal box. The dehumidification system provided by the invention can safely, efficiently, economically and automatically dehumidify equipment to be dehumidified in a substation.