Disclosed is an on-off input loop self-checking circuit based on a pulse injection method. A spike self-checking pulse is generated through control of an IO pin of a CPU and is injected to an on-off input loop, and, after the spike self-checking pulse goes through an optical coupler, the spike self-checking pulse is acquired by an ADC analog-to-digital conversion pin of the CPU and is judged; the IO pin of the CPU is connected with an input end of the optical coupler, an output end of the optical coupler is connected with an input end of an optical MOS tube, a source electrode of the optical MOS tube is connected with a common anode of a power supply, a drain electrode of the optical MOS tube is connected with one end of a safety capacitor, and the other end of the safety capacitor is accessed into the on-off input loop. After a spike self-checking pulse signal generated due to drive of the IO pin of the CPU is injected to the on-off input loop, the ADC analog-to-digital conversion pin of the CPU acquires a waveform of a secondary side of the optical coupler, processing, analyses and comparison are performed, and then a self-checking judgment for integrity of the on-off input loop is achieved; and a self-checking mode can be applied no matter an on-off signal is in any state, and the self-checking loop has the extremely high isolation capability and reliability.