The invention provides an internal supporting and flattening device for a kettle. The internal supporting and flattening device for the kettle comprises a workbench and an internal supporting and flattening mechanism. The internal supporting and flattening mechanism is fixed in the workbench and is composed of a hydraulic cylinder set, a spindle, a gear transmission unit, a cam supporting unit anda flattening component. A piston rod of the hydraulic cylinder set is connected with the spindle. The gear transmission unit comprises a motor and a transmission gear. The output end of the motor isconnected with the spindle through the transmission gear. The cam supporting unit is arranged at the front end of the spindle and comprises a supporting block and a cam. The supporting block is connected to the cam through a plurality of T-shaped blocks. The flattening component is arranged at the front end of the supporting block. According to the internal supporting and flattening device for thekettle, a workpiece is supported through a cam mechanism, and a flattening function is achieved through up-down movement of a hydraulic system, so that physical labor of workers is greatly reduced, the machining efficiency is improved, and the machining quality is ensured; and the internal supporting and flattening device has the advantages of being compact in structure and small in occupied space.