Root canal file for machine

Provided is a root canal file for a machine. A blade portion is arranged at the front end of the root canal file and fixed on a handle through a connection portion, the blade portion is formed by twisting a heteromorphic sectional cone, an annular groove is arranged on the connection portion of the root canal file, and section diameter of the connection portion at the position of the groove turns to be thin. The borne maximum torque at the position of the groove is smaller than the borne maximum torque of the blade portion. The groove is arranged on the connection portion of the root canal file, the root canal file breaks at the position of the groove due to the fact that torsion is overlarge or metal fatigues after repeated use in operation, and the connection portion is located outside a root canal so that doctors can conveniently take out the root canal.