A monitoring system for circular current of a high-voltage cable metal sheath, comprising a mobile vehicle, wherein a lifting assembly is mounted on one side of the mobile vehicle, a pushing assembly is horizontally mounted at an end, stretching out of a top of the mobile vehicle, of the lifting assembly, a detection assembly is connected to an end, away from the lifting assembly, of the pushing assembly and comprises a detection mechanism fixedly connected with an output end of the pushing assembly, and a protection mechanism is connected to one side of the detection mechanism; the detection mechanism comprises a rotary shaft which is movably connected with the output end of the pushing assembly, a fixed connecting plate which is fixedly connected with the output end of the pushing assembly is movably connected to an outer circle of the rotary shaft, a movable connecting plate which is fixedly connected with the rotary shaft is mounted on a side, away from the pushing assembly, of the fixed connecting plate, housings which are each of an arc structure and each have two ends formed with openings are fixedly connected to identical sides of the movable connecting plate and the fixed connecting plate, the two housings are opposite to each other, magnetic cores which are coaxial with the housings and are each of an arc structure are mounted in the two housings, coils which are each of a circular structure are wound on outer circles of the magnetic cores, outer circles of the coils are clad with clad layers which are fixedly connected with inner walls of the housings, contact blocks are fixedly connected to inner walls of the openings in the two ends of each of the two housings, and a wiring tube is fixedly connected to a top of the housing located on the fixed connecting plate; the protection mechanism comprises shells which are fixedly connected with outer walls of the housings, each have two ends formed with openings, and are each of a circular structure, the two shells are coaxial with the adjacent housings, protection units are mounted at the openings of the two shells, a connecting unit which is of a circular structure is fixedly connected to tops of sides, close to each other, of the two protection units in each said shell, and pushing units for opening and closing the protection units are mounted at the openings in sides, close to the rotary shaft, of the shells. the detection mechanism comprises a rotary shaft which is movably connected with the output end of the pushing assembly, a fixed connecting plate which is fixedly connected with the output end of the pushing assembly is movably connected to an outer circle of the rotary shaft, a movable connecting plate which is fixedly connected with the rotary shaft is mounted on a side, away from the pushing assembly, of the fixed connecting plate, housings which are each of an arc structure and each have two ends formed with openings are fixedly connected to identical sides of the movable connecting plate and the fixed connecting plate, the two housings are opposite to each other, magnetic cores which are coaxial with the housings and are each of an arc structure are mounted in the two housings, coils which are each of a circular structure are wound on outer circles of the magnetic cores, outer circles of the coils are clad with clad layers which are fixedly connected with inner walls of the housings, contact blocks are fixedly connected to inner walls of the openings in the two ends of each of the two housings, and a wiring tube is fixedly connected to a top of the housing located on the fixed connecting plate; the protection mechanism comprises shells which are fixedly connected with outer walls of the housings, each have two ends formed with openings, and are each of a circular structure, the two shells are coaxial with the adjacent housings, protection units are mounted at the openings of the two shells, a connecting unit which is of a circular structure is fixedly connected to tops of sides, close to each other, of the two protection units in each said shell, and pushing units for opening and closing the protection units are mounted at the openings in sides, close to the rotary shaft, of the shells.