Models-3/CMAQ and High-order Decoupled Direct Method (HDDM) was applied to simulate the ozone pollution during July 2014 in Tianjin, and then to analyze the distribution of ozone-precursor sensitivity regimes and to quantify the impact of source emissions from Tianjin and surrounding areas. The distribution of ozone concentration in Tianjin was gradually increased from the center urban areas to the suburbans areas. The concentrations in Binhai new district (in the southeast of Tianjin), was the highest. Ozone formation was mainly VOCs-sensitive in Tianjin in July, the central area (Central city, Beichen, Dongli and Binhai new district) was VOCs-sensitive over 95% days, near 2/3 of simulation days in northern suburbs (Jixian, Baodi, Ninghe and Wuqing) and Jinnan in central area was VOCs controlled, VOC-sensitive regime had similar probability of occurrence to mixed sensitive regime in southern suburbs (Xiqing, Jinghai and Dagang). Shandong Province contributed 1/4 to ozone in Tianjin, was the main source of Tianjin summer ozone, significantly influencing the level of ozone in the southeast coastal of Tianjin. The average contribute of Hebei Province was 1/6. It main effected of western area of Tianjin. Tianjin local emissions contributed in Baodi and Jixian in the north of Tianjin.