The invention aims to disclose an automatic detection device for a safety net, and the automatic detection device is used for detecting the safety net and reducing manual intervention to reduce labor intensity and improve accuracy. The automatic detection device comprises a bracket, an impact hammer and an automation tensioning mechanism used for hanging and adjusting the tension degree of the safety net, wherein the impact hammer is suspended on the bracket in a manner of moving up and down through a hoisting mechanism; the automatic tensioning mechanism comprises a frame fixed to the bracket; hooks are mounted at the periphery of the frame; the hooks on at least two adjacent side edges of the frame are movable hooks; a tension device is connected to each movable hook. The automatic detection device is designed based on the requirements of 'impact resistance tests of safety nets' of ; all operations except for net hanging and dismounting operations are automatically finished, so that the efficiency and the precision are improved; the automatic detection device is very suitable for detecting the safety net.