The invention discloses a three-phase alternating current trolley bus, which belongs to public traffic city trolley buses, and relates to a power supply system of city trolley buses; the power supply system can direct supply three-phrase alternating currents for a trolley bus sliding contact network rail. The system uses a three-phrase high-voltage power network to supply three sliding contact lines of the trolley bus through a reducing transformer or supplies railway three-phrase alternating current for two sliding contact lines. A three-phrase trolley bus acquires three-phrase alternating current from three trolley poles on the roof of a wagon box to drag the trolley bus. A three-phrase tramcar acquires three-phrase alternating current from two trolley poles on the roof of the wagon boxand iron wheels under the buses to drag the trolley bus. The wagon box of the mobile trolley bus is internally provided with a DC motor topology three-phrase fully controlled bridge thyristor speed regulating device to regulate the running velocity of the trolley bus. Compared with the existing power supply system, the power supply system of the invention has the advantages of saving investment and operating cost and saving rectification station ground and DC transmission lines and is characterized by simple system, reliable operation, energy conservation and environmental protection. Therefore, the power supply system can be widely applied to modern guide trolley buses, light rail trolley buses, trolleybuses and tramcars in cities and intercity fast dedicated channels.