The hydrocarbon accumulation conditions in LD21 Oilfield were analyzed，using mud logging，well logging，coring and core analysis test data from five aspects，including the source rocks and oil source conditions，reservoir-seal assemblage，trap characteristics，oil and gas migration and preservation condition. The results show that the crude oil in LD21 Oilfield are mainly from the source rocks of the third member of Shahejie Formation and part of them from the source rocks of the first member of Shahejie Formation. The main reservoirs are the clastic rocks deposited in the braided river in the Guantao Formation. The style of source-reservoir-seal assemblage is source at the bottom，reservoir at the middle and seal at the top. Being controlled by central strike-slip fault，the trap in the west plate is a semi-anticline structure，and in the east plate is a complex fault block structure. The long activation of the inherited faults in the Neotectonic movement creates good conditions for oil and gas migration in LD21 Oilfield. The sealing capacity of faults in the fault-controlled traps of different fault blocks is different. The oil and gas reservoirs are mainly distributed in the semi-anticline structure of west plate and the flower-like structure of east plate，which is formed under the influence of strike-slip reversal in plane. In the longitudinal direction，the oil and gas are mainly concentrated in the ⅣandⅤoil groups under the mudstone cap rock of the Guantao Formation，and the oil reservoirs discovered by single well are characterized by large thickness，long length oilbearingsections and concentrated distribution of oil layers. Finally，the oil and gas accumulation of the LD21 Oilfield in the plane and vertical is controlled by the coupling of three elements，which are strike-slip reversal，regional cap and lateral sealing of fault.