The invention relates to a capacitor thickness detection and crack feedback plate bending machine based on a PLC. The capacitor thickness detection and crack feedback plate bending machine comprises a driving motor, a clamping fixing base and a PLC host machine for controlling the driving motor. A bending shaft is installed on a motor shaft of the driving motor, and a machined piece is arranged on the clamping fixing base. The capacitor thickness detection and crack feedback plate bending machine further comprises a capacitor induction thickness detector installed on a machine frame, a pressure sensor arranged on the lateral side of a clamping groove of the clamping fixing base, a detection feedback device and a controller connected with the PLC host machine. The detection feedback device comprises an ultrasonic crack detector arranged on the clamping fixing base. The capacitor induction thickness detector, the ultrasonic crack detector and the pressure sensor are connected with the PLC host machine through a DSP module. The invention further provides a bending method. According to the capacitor thickness detection and crack feedback plate bending machine and method, sectioned machining is controlled through the PLC, the machined piece is bent at the most proper rotating speed, influences of the excessively-high or excessively-low rotating speed on the machined piece are avoided, bending cracks are reduced, and the machining quality is improved.