The invention discloses a bidirectional rectification digital quantity input port circuit, comprising a bidirectional rectification circuit composed of four diodes; a COM terminal selection circuit; an optocoupler isolation circuit composed of a first resistor and an isolation optocoupler; and a filter circuit. A common terminal at which a positive electrode of a first triode is connected with a negative electrode of a third diode is marked as a DIN terminal; the DIN terminal is connected with a positive pole or a negative pole of an external power supply; the negative electrodes of the firstdiode and the second diode are connected and then are connected with a first pin of the isolation optocoupler through the first resistor; the common terminal at which the positive electrode of the first diode is connected with the negative electrode of a fourth diode is marked as a COM terminal; the COM terminal selection circuit is connected with the COM terminal and the negative pole of an internal power supply or the positive pole of the internal power supply; the negative pole of the internal power supply is connected with the negative pole of the external power supply; the positive electrodes of the third diode and the fourth diode are connected with a second pin of the isolation optocoupler; and the filter circuit is connected between the first pin and the second pin of the isolationoptocoupler in parallel. The circuit has the advantages that an external high level input mode and an external low level input mode are supported at the same time, and the circuit cost is low.