The paper makes the simulation and analysis to the power harmonic which is produced by the AC drive device of the hot strip mill in the background of the metallurgical industry. Aiming at the line-side effects of AC-AC frequency conversion and AC-DC-AC frequency conversion control system harmonic, the paper makes the MATLAB simulation and analysis in three circumstances, such as the load parameters, the inductance value changes of transformer primary side and secondary side, and adding reactor etc., and defines the functions and value ranges of the line reactor. The simulation results can provide a design basis for the harmonic control and the power supply system when the system uses the variable frequency devices, and then improves the power supply quality of the large drag device.