The invention discloses a serial compensation device for multiple circuits. The serial compensation device comprises at least one voltage source converter, at least two serial transformers and at least one multiple-winding transformer, wherein one sides of the at least two serial transformers are in parallel connection; the other sides are serially connected with the multiple circuits; the alternating current side of the voltage source converter is connected with a parallel side bus bar of the serial transformers through the multiple-winding transformer, so that a power flow function of one or more converter averaging system is realized. The device provided by the invention can be independently mounted on a power transmission system and serve as a static synchronous serial compensator and also can be served as a constituent part of a unified power flow controller, a convertible static compensator, a space power flow controller and a unified power quality regulator in serial connection with the power transmission system device. The device can save the capacity of the converter, can increase the application efficiency of the serial compensation device and can reduce cost and occupied area.