The invention discloses an over-current protection circuit of a direct-current electronic contactor, which is characterized in that a drain electrode of an NMOS switching transistor is connected witha positive electrode of a direct-current power supply, and a source electrode is connected with a negative electrode of the direct-current power supply through a load; and a control signal of a single-chip microcomputer is input into a grid electrode of the NMOS switching transistor through a driving circuit. Multiple paths of the NMOS switching transistor are connected in parallel. The drain electrode of the NMOS switching transistor is connected with a non-inverting input end of a differential amplifier through a relay protection circuit and a differential resistor, the source electrode ofthe NMOS switching transistor is further connected with an inverting input end of the differential amplifier through a relay coil equivalent resistor and a differential resistor, and the output end ofthe differential amplifier is connected with an AD conversion module of the single-chip microcomputer. The driving signal controls the NMOS switching transistor to be switched on. The over-current protection circuit samples voltage at the drain electrode end and the source electrode end of the NMOS switching transistor, and when the voltage exceeds a set threshold value, over-current shutdown protection is performed. The over-current protection circuit is simple in design, the use cost of the circuit can be reduced, and the reliability and the stability of the circuit during working can be improved.