Abstract：Diabase intruded into multi-horizon of the northern slope of Gaoyou Sag makes the structural conditions and the petroleum geology conditions of broken block area more complex. The formation period of diabase closely related to the hydrocarbon reservoir formation has become a deeply concerned problem. Diabase is identified and interpreted by core observation, thin section identification, well-drilling, well-logging, and seismic data, it shows that logging response characters of the diabase in the northern slope are low natural gamma ray, low acoustic, low neutron porosity, high density, and high resistivity, its characteristics with the seismic reflection profiles are low frequency, strong amplitude, and good continuity, the upper sets of diabase are intruded into the fourth member of Funing Formation to Sanduo Formation and the lower sets of diabase are intruded into the second member to the third member of Funing Formation. Based on the above facts, with fault distribution of the corresponding period, the analysis results indicate that distribution range of the upper sets of diabase is more centralized, and is mainly along the major faults in north east direction and east west direction, and the lower sets of diabase is more extensive, and is obviously controlled by the transfer zone of major faults. According to the isotopic dating, and by comprehensively consideration of every factor involving spreading range, distribution characteristics of thickness, and tectonic activity of different stages, it is concluded that the upper sets of diabase are the products of Sanduo Event, and the lower sets of diabase are the products of Wubao Event and Sanduo Event.