Based on least squares collocation, adaptive fusion algorithm based on observation signals is deduced. The airborne gravity data, satellite gravity data and land gravity data of Bohai bay area are combined by the adaptive fusion algorithm based on observation signals. The accuracy of gravity observation data is improved after fusion. Tectonic stress field in Bohai area is inversed using gravity observation data after adaptive fusion.Combined with earthquake historical data, tectonic stress field in Bohai area is analyzed. Characteristics of Tectonic stress field in Bohai area are summarized. There is a close relationship between gravity and tectonic stress. The direction of tectonic stress field is towards the north.Tanlu and Zhangjiakou-Penglai Fault zone are consistent with tectonic stress field in Bohai area. Tectonic stress is gathered in high degree in these Fault zone. And the value of tectonic stress is higher than others as well.It is showed that the tectonic movement is active in Tanlu Fault and Zhangjiakou-Penglai Fault from Tangshan to Zhangjiakou, corresponding with historical earthquake data.