Oil and gas exploration of the Majiagou Formation in the Daniudi area, Ordos Basin, continues to make breakthroughs. Practice has shown that the whole Fifth member of the Majiagou Formation (Ma5) contains gas, but its multiplicity of reservoir types and complex genetic backgrounds have not been conducive to classification prediction. To systematically summarize the reservoir genetic types in this study, the reservoir space types and main influences on reservoir development were investigated by core observation, thin section identification, cathodolumines-cence thin section observation, whole-rock X-ray diffraction analysis and carbon and oxygen isotope analysis. These demonstrate that, in the study area, the Ma5 reservoirs contain intercrystal pores, intercrystal dissolution pores, microcracks, residual intergrain pores and intragrain dissolution pores. The reservoir developed in a confined evaporative platform as a result of seepage-reflux dolomitization. Epigenetic karstification had no obvious influence on the reservoir in the Ma₅⁵ submember. Genetic analysis in the study area suggests four types of reservoir: gypsum-dissolved, weakly re-formed fractured dolomite, powder-crystal dolomite and syngenetic dissolution granular reservoirs, with gypsum-dissolved reservoirs and powder-crystal dolomite reservoirs being the main types. Gypsum-dissolved reservoirs are related to the salinity of the sedimentary environment and karstification during the supergene period, and contain mainly gypsum mold pores. Powder-crystal dolomite reservoirs are the result of seepage-reflux dolomitization during the period of sea-level decline, and the reservoir space consists of intercrystal pores. This summary is significant as a guideline for subsequent high-quality reservoir predictions in the Ma5 member in the Ordos Basin.