The Ordovician pre-salt dolomite reservoir is an important replacement field for natural gas exploration in Ordos Basin. Based on drilling core, thin section, physical analysis, geochemical characteristics and other related information, the characteristics, genesis and distribution of the Ordovician pre-salt dolomite reservoir are systematically studied by using the method of multi-parameter analysis in micro-region. The results showed that: (1)The granular shoal dolomite reservoir and microbial dolomite reservoir are mainly developed in the Ordovician pre-salt. The reservoir lithology of granular shoal dolomite is arenaceous dolomite, oolitic dolomite and very fine-fine crystalline dolomite, the pore space is composed of dissolved pores, intergranular pores, intercrystal (dissolved) pores and fractures, and the average porosity is 6.04,. The lithology of microbial dolomite is thrombolite dolomite, the pore space is composed of dissolved pores, dissolved vugs and micro-fractures, and the average porosity is 5.64,. (2)The pores of the Ordovician pre-salt reservoir inherited the primary pores of granular shoal and microbial dolomite which suffering from the dissolution, dolomitization, the mineral filling of gypsum, salt, quartz, finely-medium crystalline dolomite and calcite. (3)It is predicted that the favorable reservoir is mainly distributed in the central paleo-uplift, the Hengshan uplift belt and the low uplift zone of Wushenqi depression.