The embodiment of the invention provides a protective device for a knife-switch and a knife-switch system. The protective device for the knife-switch comprises a phase sequence determining module and an output control module, wherein three input ends of the phase sequence determining module are respectively connected in parallel with three-phase output ends of a motor power supply of the knife-switch, so as to collect three-phase output voltage of the motor power supply in real time and determine the phase sequence of the motor power supply according to the collected voltage; the input ends of the output control module are connected with the output ends of the phase sequence determining module; output terminals of the output control module are connected in series with a control circuit of the knife-switch, so as to cut off the control circuit when the phase sequence determining module determines the phase sequence of the motor power supply as a negative phase sequence. The technical solution can be used for avoiding the switching operation of the knife-switch under the action of the negative phase sequence voltage of an external power supply, further avoiding the motor stalling phenomenon of the knife-switch and reducing the damage of a link mechanism or a motor.