The invention discloses a main loop wiring structure of a compensator. According to the structure, a parallel converter is connected to a three-phase bus of a power grid through a parallel transformer. A series converter is connected to a line through a series transformer. The parallel converter is connected with the series converter through DC positive and negative buses. A bridge-connection bypass switch is respectively arranged at the two ends of the line-side winding and the two ends of the valve-side winding of the series transformer. A switch is respectively arranged on the incoming wireand the outgoing wire of the line-side winding of the series transformer. A starting circuit is located between a parallel valve-side switch and a parallel flow converter. A thyristor bypass switch is connected between series transformer valve-side windings in a bridging mode. According to the invention, the accurate adjustment on the power flow of the line can be achieved, and the control response speed is fast. Meanwhile, the transient stability and the steady-state performance of the system can be improved. The reactive power of the line can be independently controlled. The reactive poweris kept unchanged when the active power of the line is adjusted, or the reactive power of the line is adjusted according to the demand of the power grid. Therefore, the power transmission performanceof the system is improved.