The invention relates to an automatic cleaning device for gaps in cement fiberboards, a building decoration material, which includes a lifting platform, a bottom plate, a filling device, a leveling device and a brushing device. There is a leveling device, and a brushing device is installed at the rear end of the bottom plate. The brushing device includes racks, gears, rotating motors, pallets, sliders, linear slide rails, lifting electric push rods, auxiliary telescopic rods, steering motors, steering panels, Move the slide rail, push the electric push rod, connect the support and the gap cleaning mechanism. The invention can solve the problems of high labor intensity, high labor cost, hidden safety hazards, uneven filling and low work efficiency existing in the existing cement fiberboard gap cleaning technology, and can realize the function of automatically cleaning the cement fiberboard gaps.