The invention provides a method for detecting a defective part. An image acquisition device collects image information of a to-be-detected part and transmits the image information to a central controldevice; edge information is compared with standard image edge information of the to-be-detected part; if the edge information is consistent with the standard image edge information, the central control device controls a drive motor to work and turns off a motor and a striking mechanism, a conveying belt transports the to-be-detected part to a product packaging position; otherwise, the central control device controls the drive motor to work and turns on a laser transmitter arranged at the striking mechanism, a laser receiver receives a laser signal, the central control device controls the drive motor to stop working and controls the motor to drive the striking mechanism to mark the defective part, the central control device controls the drive motor to work, and the conveying belt transports the to-be-detected part to a product scrap position.