Abstract: It is recognized that，by means of researching the characteristics of the structure，fault sealing properties，sedimentary facies，reservoir and interlayers thickness of Shaxi N¹-N¹₂ beds，the Shaxi N¹-N¹₂ structure is a complex nose-like one，there are 15 faults in target beds，among which，，faultⅡ，(2)，(7) and ( 9) are better in sealing properties than others，the main active period of the fault were N²₂-N³₂，upwards，Shaxi N¹-N¹₂ is a set of reserve cycle deposition composed of lacustrine transmitting braided river delta，the deposits were mainly from west and northwest area，and controlled by north Alar River sedimentary system，the reservoir in hanging wall of fault Ⅱ belongs mid-porosity and permeability and the reservoir in footwall to low porosity and permeability，the amount of cements and grain maturity in reservoir in hanging wall are worse than the one in footwall，and the intergrain porosity in hanging wall are much higher than the one in footwall.It is concluded based on the evidence mentioned above that the main controlling factors that hydrocarbon productivity in hanging wall of fault Ⅱ is higher are structural faulting，reservoir porosities and the types of porosity，that main controlling factors that hydrocarbon is rich in Ⅵ-Ⅷ pay zones are structural characteristics，fault sealing properties，interlayers thickness and sedimentary characteristics.

Key words: Shaxi area, N¹-N¹₂ reservoir, fault sealing, main controlling factors, interlayer, Qaidam Basin