Excess load automatic protection and braking device

An excess load automatic protection and braking device comprises a direct-current power source, a controller, an electromagnetic valve and a load sensor, wherein the controller and the electromagnetic valve are installed in an operation chamber of an operation machine, and the load sensor is installed on a steel wire rope of a roller of the operation machine and is moved above a weight indicator in the middle of the fixed end through a fixed pulley of an overhead traveling crane of a derrick and a movable pulley of a large crane. The direct-current power source of the operation machine is connected with the controller, and terminals of the controller are connected with the electromagnetic valve and the load sensor respectively. The electromagnetic valve is connected with an air circuit control pipeline of a brake of the operation machine in series, the load sensor collects signals and transmits the signals to the controller, control signals of the controller are transmitted to the electromagnetic valve, and t