The invention belongs to the field of a sheet metal component production processing device, and mainly relates to a plate flanging mechanism. The plate flanging mechanism is characterized in that an upper flanging knife (29), a lower flanging knife (30) in a flanging knife structure are respectively positioned above and under a processed workpiece and are symmetrically arranged from top to bottom; an output shaft of a rotating oil cylinder in a driving mechanism is connected with a coupler, one end of a rotating arm is used as an action point, fixedly connected with the coupler and hinged to a rack through a rotating shaft; the other end of the rotating arm is fixedly connected with a flanging knife beam; the flanging knife beam drives the flanging knifes to do arc motion by using one end of the rotating arm as a circle center, and a plate can be upwards or downwards bent. According to the plate flanging mechanism disclosed by the invention, the plate needing to be processed can be subjected to rotary bending by adopting an upper and lower flanging knife structure, the situation of bending the plate in two directions in different angles on the condition of same feeding can be realized, the auxiliary time is effectively shortened, and the working efficiency is increased; the bending and the flanging in different angles can be carried out at the same time, the operation is flexible, and the size accuracy can be ensured.