Middle Ordovician Majiagou541 Submember is one of the main nature gas pay horizons in Jingbian Gas Field, Ordos Basin. 3 subfacies and 8 microfacies assemblages have been recognizes according to the petrologic characteristics and Sedimentary Structures. By analysis of physical data, it is considered that the structures and properties of the reservoir rock show intensive heterogeneity. Microcosmically, it mainly shows microfine throats and fine throats with low porosity and low permeability. Longitudinally, it shows abnormal rhythm, random rhythm and homogeneous rhythm modes. Horizontally, it shows nonuniformity in average porosity and permeability presented in lateral development. The difference of sedimentary microfacies and microfacies assemblages is the basis for controlling rock pore development. Diagenesis determines the extent of pore development. Karst palaeo-landform styles obviously restrains to the reservoir distribution. All of these common processes eventually lead to the lateral heterogeneity in reservoirs.