The west coast of Taiwan Strait has complex stress field characteristics, under the interaction of the Eurasian plate, the pacific plate and the Philippines plate. And in situ stress state in the area is not well researched. In order to further study the in situ stress characteristics, the authors measured the magnitude and direction of in situ stress in Pingtan and Raoping through hydraulic fracturing, and discussed the tectonic stress field characteristics of the western coast of Taiwan Strait on the basis of previous study and focal mechanism data. The study shows that the dominant directions of the maximum principal stress in Pingtan and Raoping are N19°W and N37°W. And analysis based on focal mechanism data suggests that the stress field in the study area has fan-like distribution originated from NNW and expanded to EW. In situ stress state in horizontal direction is roughly divided by Shaxian-Nanridao fault, stress of northern areas is low, but stress of southern areas is high. And in situ stress level gradually decreases from north to south, starting from fault zone in the downstream area of Jiulongjiang. Three boreholes were selected in Pingtan, Quanzhou and Raoping，and Coulomb friction criteria was employed to study the fault activity of these three boreholes. It is considered that fault activity of northern areas of Western Taiwan Strait at low stress level is weak. In situ stresses in middle areas of Western Taiwan Strait, where Quanzhou is located, have accumulated to a high level. Therefore, faults in this area have a high possibility of unstable sliding. Faults in adjacent areas of Raoping is unlikely to slide unstably in the near future.