By coupling ozone source apportionment technology (OSAT) with comprehensive air quality model with extensions (CAMx), the regional transport matrix of surface O₃ was built and the spatio-temporal distributions were also analyzed in 13 cities of Jing-Jin-Ji Region in July, 2015. Results showed that the major contributor to O₃ was transport source (TS>80%), while the local source (LS) contributed only 6.9% in Langfang and 19.7% in Beijing. The transport source included in-region sources (IRS, ranges from 10.3% in Cangzhou to 32.2% in Langfang), out-region sources (ORS, ranges from 37.3% in Chengde to 60.7% in Qinhuangdao), and boundary condition (BC, ranges from 14.4% in Handan to 23.1% in Zhangjiakou). The daily matrix of regional transport in key cities also showed the significance of ORS to O₃. There was a positive correlation between LS contribution and the mass concentrations of O₃-8h, in particular, the contribution of LS increased significantly during high ozone episode days. Regarding the regional characteristics of transport path to different cities, the ozone levels were influenced by both local and regional emission sources, and joint efforts are required to optimize the O₃ reduction scheme.