The Pg travel time picked from three sea area lines,which were completed in southwestern Taiwan Strait in 2014,were used to reconstruct basement velocity structure,topoqraphy and depth of upper crust along the profile by means of finite difference layer imaging of travel time. The minimum and maximum basement depths of three profiles are between 1.5km and 4.2km. Although there are some changes in basement depth,the fluctuation is obvious only in the local area,which shows the structure of fracture or depression in the upper crust. By comparison with geological structure zonation of the Taiwan Strait,it shows no more difference between the basement structure which is obtained from inversion and the geological structure of the seismic profile across this area. The travel time tomography results also provide reliable shallow layer velocity information for follow-up inversion of the deep structure.