The invention discloses a secondary sedimentation tank with a self cleaning function. The secondary sedimentation tank is provided with a tank body, a mud discharging system and a self cleaning system, wherein the tank body is in a rectangular shape; the side edge of the tank body is provided with a water inlet ditch; water outlet ditches are arranged at the inner side of the water inlet ditch inparallel; a pollution discharging groove is formed in one end, far away from the inlet of the water outlet ditches, in the tank body; the mud discharging system is formed by a plurality of groove-shaped mud storage hoppers arranged on the bottom surface of the tank body; a mud discharging pipe with holes in the pipe wall is arranged in each groove-shaped mud storage hopper; the self cleaning system is a slag scraping cleaning plate arranged on the water storage water level in the tank body; an anti-sticking coating containing repulsion buffer agent is arranged on the surface of the slag scraping cleaning plate; a slag scraping motor driving the slag scraping cleaning plate is installed. The secondary sedimentation tank disclosed by the invention has the self cleaning function; dirty articles such as floating slags on the water level of the secondary sedimentation tank can be conveniently cleaned; a great amount of labor and materials required by a conventional manual cleaning mode is saved; the water outlet quality is improved; in addition, the slag scraping plate using the anti-sticking design has no need of the afterwards complicated cleaning work procedures.