The invention relates to an automatic blocking preventing device for a separation plate of a garbage compressor. The automatic blocking preventing device comprises a compression spring, a space occupying block, an outer baffle plate and an outer baffle frame, wherein the middle part of the outer baffle plate is provided with a spring fixing seat, the middle part of the space occupying block is provided with a spring installing sleeve in a way of corresponding to the spring fixing seat, one end of the compression spring is arranged in the spring fixing seat, the other end of the compression spring is arranged in the spring installing sleeve, and the outer baffle frame is arranged at the edge of the outer baffle plate. After a middle gate ascends, the space occupying block of the automatic blocking preventing device is automatically pushed out from the compression spring, the vacancy of a door groove is occupied, pushed garbage is prevented from being left in the door groove, and the hardship that sanitation workers enter hot and smelly box bodies for cleaning is omitted. The automatic blocking preventing device has the advantages that the design is simple, the external energy is not needed, the work efficiency is high, and the maintenance is convenient.