The invention discloses an automatic feeding device of a punching machine. The automatic feeding device comprises a punching machine main body, an operation platform and a hydraulic cylinder, whereinthe hydraulic cylinder is started; the hydraulic cylinder drives a hydraulic rod, and a material pushing plate at the tail end of the hydraulic rod pushes out a raw material to be punched at the bottom of a supporting plate through the pushing of the hydraulic rod; the raw material to be punched is pushed out by the material pushing plate and then falls onto the operation platform; a weight sensordetects the weight of the raw material to be punched, after an infrared sensor body and an infrared sensor II sense the raw material to be punched, the information is transmitted to the punching machine main body; and after the punching machine main body is received the data of the weight sensor, the infrared sensor body and the infrared sensor II, a punching operation of the raw material to be punched which is on the weight sensor is carried out. According to the device, the punching machine continuous working performance on the raw material is high, the convenience for feeding of the punching machine equipment is improved, the accuracy of the feeding of the raw material to be punched is improved, and the working efficiency of the punching of the punching machine is improved.