Abstract: To avoid stray current and maintain the benefit of no phase-split in the DC traction power supply system, an AC traction power supply system was proposed for the urban public transport such as metro and light rail transit. The proposed system consists of main substation (MSS) and cable traction network (CTN). MSS includes a single-phase main traction transformer (MTT) and a negative sequence compensation device (NCD), while CTN includes double-core cables (DCC), traction transformers (TT), overhead catenary system (OCS), rails (R), etc. Three key techniques of the proposed system were discussed. First, power supply principle, equivalent circuit and transmission ability of CNT were introduced and cable-catenary matching technique, catenary voltage level selection were discussed. Second, the segmentation technology, status identification method for traction power supply network, distributed and centralized protection schemes, etc. were discussed. Third, single-line main substation supply scheme, and two or more lines shared main substation scheme were presented. Given that the excellent technical performance, good economy and high reliability of the proposed system, it provides a new alternative for metro and urban rail transit power supply system.