The embodiment of the utility model discloses a small animal prevention alarm device suitable for an outdoor mechanism box or a terminal box, which is used for solving the technical problem that smallanimals often enter the existing outdoor mechanism box or the terminal box to influence equipment in a box body. The embodiment of the utility model comprises a control module, an infrared module, anacousto-optic module and a power supply module, the infrared module and the acousto-optic module are connected with the control module. The control module, the infrared module and the acousto-optic module are all connected with the power supply module; the infrared module comprises an infrared emitter and an infrared receiver which are arranged in the box body, and the infrared emitter sends infrared light to the infrared receiver to form an infrared warning line. In the embodiment, the infrared emitter in the box body emits infrared light to the infrared receiver to form an infrared warningline, and when a small animal enters the box body to divide the infrared warning line, the control module controls the acousto-optic module to emit light and sound to drive the small animal to leave the box body.