Abstract: On the top of the Ordovician, the weathering crust reservoir in the upper combination of Majiagou Formation (M5₁ and M5₄) is the main gas reservoir of Lower Palaeozoic in the eastern part of Sulige gasfield. The M5₁₊₂ and M5₄¹ are the major gas production reservoir in this gasfield. Based on previous researches, the authors conducted studies including core observation, indoor thin-section analysis, scanning electron microscope and cathode luminescence. Conclusions have been drawn that the main rock type is cream powder-mud powder crystal dolomite, and the main reservoir space type is gypsum hole and karst seam; the reservoir is controlled by sedimentation, diagenesis, lava palaeo-geomorphology and tectonics; sedimentation and diagenesis are the main controlling factors, the favorable sedimentary facie is the basis of reservoir development; diagenesis determines the final formation of reservoir space; the structure of reservoir affects the reservoir communication and infiltration; the karst geomorphology controls the development degree of the reservoir space and reservoir preservation condition in a larger sense.