The invention relates to a bottom face cleaning device of a full-automatic cleaning machine. The bottom face cleaning device comprises a waterproof cover, a cleaning motor, a drive shaft, a brush disc and two L-shaped limiting rods. An opening is formed in the bottom end of the waterproof cover, an output shaft of the cleaning motor is fixedly connected with the upper end of the drive shaft through a coupler, and the cleaning motor provides drive force for the bottom face cleaning device. The drive shaft penetrates through the opening in the waterproof cover and is connected with the waterproof cover through a bearing, and the brush disc is fixedly connected to the lower end of the drive shaft. The two L-shaped limiting rods are symmetrically located on the two sides of the waterproof cover, the upper ends of the L-shaped limiting rods are fixedly connected with the waterproof cover, limiting blocks are arranged at the lower ends of the L-shaped limiting rods, the limiting blocks achieve the effect of limiting the motion trail of the brush disc, the limiting blocks and annular limiting grooves in the brush disc are connected in a sliding fit mode, the phenomenon that the brush disc swings leftward and rightward due to vibration is avoided, and the cleaning efficiency is improved. The bottom face cleaning device can quickly clean a compartment and has the advantages of being high in cleaning speed and good in cleaning effect.