This paper analyzes the geologic conditions of hydrocarbon accumulation in the Chang -9 reservoir of Ordos Ba-sin.The oil in the Chang-9 reservoir is mixed oil sourced from both the overlying Chang-7 and Chang-9 itself.However, oil in the Chang-9 reservoir in Zhidan area is only sourced from Chang-9 source rocks ,without any contribution from the Chang-7 source rocks .The oil mainly occurs in the first segment of Chang-9 oil reservoir .Reservoirs are mainly of distrib-utary channel sandstone of braided river delta plain facies and underwater distributary channel sand of delta front facies , with some turbidites of semi-deep lake facies.Lithology of Chang-9 reservoir is dominated by lithic arkose with well-de-veloped primary inter-granular pores,low porosity and permeability.The physical properties of the Chang-9 oil reser-voirs show great lateral variation.In Jiyuan area, the sandstone feature in coarse grain, well-developed inter-granular pores and good poroperm characteristics.In contrast,in Luochuan area,the carbonate cemented sandstone has poor po-roperm characteristics due to poor development of pores .According to the relationship between source rocks and reser-voirs,two source rock-reservoir combination patterns were identified in Chang-9 oil reservoirs, i.e.“upper sourcing”pattern and “indigenously sourcing” pattern.Jiyuan area is the most favorable for further exploration based on compre-hensive analysis.% 通过对鄂尔多斯盆地长9油层组成藏地质条件的分析，认为长9油藏的油源主要来自于上覆长7油层组和其本身两套烃源岩，但志丹地区长9油藏原油来源于长9烃源岩，无长7烃源岩的混入。长9油层组含油段主要集中在长91亚段，储集体主要发育于辫状河三角洲平原相分流河道砂体及三角洲前缘水下分流河道砂体，部分为半深湖亚相浊积岩砂体。长9储层的岩石类型主要为岩屑长石砂岩，以粒间孔为主，孔隙度、渗透率总体较低。平面上储层物性分布差异性较大，姬塬地区砂岩粒度粗，粒间孔发育，物性最好；而发育碳酸盐胶结物的洛川地区孔隙不发育，物性最差。根据源－储关系，长9油层组主要发育上生下储、自生自储两种成藏组合类型。据综合分析，姬塬地区成藏条件较好，为下一步勘探的最有利区。
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