There are two sets of Ordovician carbonate reservoirs developed in Maigaiti slope in Tarim basin: the Middle? Upper Ordovician limestone is a fractured reservoir mainly controlled by multistage fault activity and fault? related karstification, and favorable reservoir rocks are mainly distributed in fracture? developed area; the Lower Ordovician dolomite is a fractured? vuggy reservoir chiefly controlled by burial recrystallization, burial karstification (organic acid and hydrotherm), which is distributed in Well Q5 and Well S1 3D seismic areas as well as carbonate platform in western Tarim basin, with seismic reflection characteristics as “beads”. The distribution of the reservoir rocks indicates that the Lower Ordovician dolomite reservoir is the breakthrough for hydrocarbon exploration of the Ordovician in Maigaiti slope