A fluid electricity generation device with dual-case includes a stator assembly and a rotor assembly arranged in the stator assembly. The stator assembly includes an outer case and at least one magnetically permeable unit disposed on the outer case. The rotor assembly includes a rotating member and at least one magnetic module. The rotating member has an inner case, a column arranged in the inner case, and a spiral blade connected to the column. The rotating member is rotatable with respect to the outer case. The first magnetic module is disposed on the inner case and has a magnetic area. The spiral blade is configured to be driven to rotate the rotor assembly by utilizing fluid, such that the magnetic area can pass through the magnetically permeable unit for generating induced current.