Abstract: Based on core, thin section, geophysical and testing data, the fracture development in the Paleozoic reservoirs in the western Bachu Uplift was studied. It was concluded that fractures were most developed in Carboniferous, and second in Ordovician, and least in Silurian and Devonian. The fractures were usually structural ones, among which the oblique fractures were most common, followed by the horizontal and vertical fractures. The fractures in Carboniferous were half-filled by calcite, dolomite, terrigenous clastic and anhydrite, etc, while those in Ordovician were filled or half-filled by calcite and shale. The development of the fractures was controlled by tectonic stress and position, fault, lithology, thickness and rock combination. Fractures could not only improve reservoir performance, but also help karstification and create favorable conditions for the formation of se-condary pores. Fractures were also an important medium in the process of oil and gas migration and accumulation, and controlled oil and gas accumulation.