This invention relates to the field of centrifugal fans, specifically disclosing a portable energy-saving electric fan and its usage method. The fan includes a housing with a grille and a fan installed inside the housing. The fan's outlet is aligned with the grille. The top of the housing has an opening through which the fan can extend. The fan's outer casing is divided into a fixed part and at least one movable part. The movable part is movable relative to the fixed part. When the movable and fixed parts are separated, maintenance tools can be inserted into the casing to inspect the inner wall and
impeller. This invention allows the fan to be lifted from the housing for easy maintenance. Furthermore, the fan's outer casing can be divided into a fixed part and at least one movable part, and the fixed and movable parts can be fixed to the fixed part without connecting parts, only by a retaining element inside the housing, facilitating maintenance and return to its original position after maintenance.