Abstract: Based on the matrix raster data of whole China, using costweighted distance algorithm with ArcGIS 9.3 platform, this paper quantitatively analyzed the positive role of the improvement of traffic accessibility in China due to the construction of Bohai Sea Straits Passage(BSSP). The study shows that the costweighted distance algorithm is scientifically and accurately suitable for the traffic accessibility comparison of preand post great infrastructures. The “China effect boundary” of BSSP is the southern area of the “Xuanhui River estuary of Hebei provinceGaolan county of Ningxia Hui autonomous regionShache county of Xinjiang uighur autonomous region” line and the northern area of the “Suizhong county of Liaoning provinceDongwuzhumuqin banner of inner mongolia autonomous region” line. After the construction of BSSP, the time cost between the two sides of BSSP decreases much and the accessibility area of the node cities increases significantly, which follows the spatial decline law. The accessibility impact on coastal cities of BSSP is more than that on inland cities, and that on the southern area of Yangtze river is more than that on the Northeast.