The invention relates to a building evacuation door opening device and relates to the technical field of safety doors. The building evacuation door opening device comprises a door frame, a door, an air cylinder, a push rod, a connecting rod, a side plate, fixed pulleys, a steel wire rope and a heavy object. The door frame is hinged to the door, the air cylinder is mounted on the door frame, and the air cylinder is in driving connection with the push rod. The push rod is hinged to the connecting rod, one end of the connecting rod is connected with the door, and the side plate is connected to one side of the door frame and fixedly provided with the three fixed pulleys which are arranged in a triangle shape. The steel wire rope winds across the three fixed pulleys, the heavy object is fixed to one end of the steel wire rope, and the other end of the steel wire rope and the door are fixed. According to the building evacuation door opening device, a power source is automatically cut off ina disaster by a firefighting system, and meanwhile the door is automatically opened; the door is opened in time, safety is good, and the door can also be automatically opened when people pass throughthe door; and the building evacuation door opening device has the advantages that the structure is simple, arrangement is reasonable, and the manufacturing cost is low.