The invention discloses a meshing transmission filter for purifying fondant of a plastic extrusion system. The meshing transmission filter comprises a feeding end machine body and a discharge end machine body, wherein a filtering net plate is arranged between the feeding end machine body and the discharge end machine body through rotating a center shaft; teeth are arranged on the circumference edge of the filtering net plate, a transmission gear is meshed with the teeth of the filtering net plate, and the transmission gear is connected with a one-way transmission device through a transmission gear shaft; the one-way transmission device is connected with a pneumatic driving device through a rotating rocker arm, the pneumatic driving device comprises a driving air cylinder, and the driving air cylinder drives the rotating rocker arm to reciprocate around a hinged shaft point, when the rotating rocker arm is in a rotating process, the rotating rocker arm is controlled by the one-way transmission device, so that the rotating rocker arm can drive the transmission gear shaft to rotate along the same direction all the time, and the filtering net plate is enabled to rotate around the self center shaft along a feeding direction all the time through the meshing transmission; and a condition that a new filtering net channel and an old filtering net channel are alternately replaced is realized.