The invention discloses a shearing line automatic knife changing device which comprises an intelligent control device, a knife rest device, a manipulator device, an electrical device and a protectivedevice. The intelligent control device comprises a robot and a robot sliding table, and the robot controls the manipulator device and the electrical device to work according to instructions; the robotsliding table is a robot moving rail, and the knife rest device is composed of a knife rest and knifes; the lower end of the knife rest is provided with four vertical columns which are fixed to the ground in a supported mode, and a storage platform of the different knives is arranged above the knife rest; the manipulator device is divided into pickup devices and takedown devices, and the pickup/takedown devices are located on the two sides of a shearing production line; each pickup/takedown device is composed of a pickup/takedown frame, a linear motor, an air cylinder pressing mechanism, a pneumatic suction cup and a detecting system; and the electrical device is an electric control system; the protective device is constituted by protective guards on the periphery. According to the shearing line automatic knife changing device, the replacing precision of the shearing line knifes can be improved, meanwhile the labor intensity of a worker is relieved, and the working efficiency is improved.