The invention discloses a reliability detecting device for a slot type photoelectric sensor. The reliability detecting device comprises main test box being a main box and an expandable sub test box being a sub box. In the main box, a connecting rod and a motor output shaft are fixedly connected; and a motor is fixedly connected with a motor fixation bracket fixed on a box bottom boss. Two DB25 connectors and a lock catch connected to the sub box are arranged at the outer side of the main box body. A sensor wiring terminal, a collision bead lock and a limiting column are arranged at an upper cover plate arranged at the main box body. The main box is provided with a main box cover connected with the upper cover plate by the collision bead lock. A light cutting plate adjusting piece is arranged on a light cutting plate; and the light cutting plate is in loose connection with the connecting rod and then is placed on the limiting column. The sub box does not includes a driving part and therest parts of the sub box have the same structures as the main box. According to the invention, with a sealing manner, simulation of detection in severe environments like high temperature, low temperature, high humidity and dust environments can be performed in open space or an environment test box. When the number of to-be-tested sensors is larger than the measurable number of the main boxes, subboxes can be connected for extension. The device has advantages of reasonable overall structure and high reliability and practicality.