Disclosed is an automatic flushing type pre-filtering device, that includes: a valve head set, a filter cartridge set, a movable rod piece, and a drain valve set. The filter cartridge set includes: a cylinder body; a filter cartridge, disposed in the cylinder body, the filter cartridge includes a filter net rack and a filter net disposed on the filter net rack. A first chamber is formed between the filter cartridge and the cylinder body, and a second chamber is formed inside the filter cartridge. The movable rod piece is provided with a hollow portion inside, and the movable rod piece is disposed in the second chamber. A water separation piece is disposed between the movable rod piece and the filter net rack. A plurality of through holes are disposed on the movable rod piece corresponding to a position of the second chamber.