The utility model discloses an interlocking mechanism for locking an auxiliary fracture of a main fracture of a pole-mounted switch. The mechanism comprises a mechanism side plate which is perpendicular to a main shaft of the circuit breaker, an interlocking plate moving up and down along the mechanism side plate is arranged in the middle of the mechanism side plate; an isolating switch mechanismis arranged on the lower side of the interlocking plate, a crank arm is arranged at the upper end of the interlocking plate, one end of the crank arm is connected with the interlocking plate, the other end of the crank arm makes contact with the side of a cam, the cam sleeves the breaker spindle and rotates synchronously with the breaker spindle, and the cam drives the interlocking plate to move up and down through the crank arm. A limiting pin is arranged at the lower end of the interlocking plate and makes contact with the isolating switch mechanism. By arranging the interlocking mechanism with the structure, the mechanism structure of locking the auxiliary fracture of the main fracture of the pole-mounted switch is simplified, so that the interlocking mechanism is extremely easy to realize and manufacture, the production efficiency is greatly improved, and the production cost is reduced. The interlocking mechanism can effectively prevent misoperation of the isolation switch, and ensures power utilization safety.