The invention discloses a self-adaption on-off input circuit of electric power secondary equipment. The self-adaption on-off input circuit comprises a CPU with an ADC or an ADC and a CPU which are discrete devices, and also comprises an on-off dc power supply monitoring circuit, an on-off signal input circuit and a temperature monitoring circuit. The ADC has a plurality of sampling channels which respectively take samples of the output analog quantity of the on-off signal input circuit, the on-off dc power supply monitoring circuit and the temperature monitoring circuit. The self-adaption on-off input circuit of the electric power secondary equipment can adjust the on-off input voltage motion threshold value through software in a self-adaption manner, can monitor the state of the on-off power supply, and is characterized by being low in hardware cost, convenient in software maintenance, good in fault-tolerant and anti-interference performances and wide in application field, and being suitable for the industrial-grade operating temperature environment.