A power on and off testing device includes a control module, a switch module, an alternating current and direct current converter module, an input module, and a detecting module. The switch module is connected to an alternating current source. The alternating current and direct current converter module is connected to a motherboard of a computer. The input module is connected to the control module to input testing references to the control module. The detecting module is connected between the control module and the motherboard. The detecting module detects a power status of the motherboard and sends the power status to the control module. The control module controls the switch module to be switched on according to the power status after receiving the testing references, thereby controlling the alternating current source to supply power to the motherboard.