Abstract: The gas reservoir of He-8 Member in Mizhi Gasfield of Changqing Oilfield has OOIP of 789.8×10⁸ m³ and its degree of reserve recovery is less than 1%, so it is an important block with the potential of productivity construction. Its single sand body is thicker, but its reservoir physical properties are poorer, the effective gas layers are thinner and the distribution laws of gas-rich reservoirs are not figured out, so the drilling effects are poorer. In order to speed up the productivity construction in Mizhi area, it is necessary to refine geological understanding and potential evaluation, search for favorable zones and optimize well locations. The distribution characteristics of gas bearing sand bodies in each sublayer are depicted precisely by analyzing the sedimentary microfacies of each sublayer. Then, the reservoir classification standard was formulated by means of the clustering analysis method by studying the microscopic characteristics of reservoir cores. On the basis of sedimentary microfacies control, the distribution characteristics of dominant reservoirs were clarified. Afterwards, the favorable drilling zones were selected by means of the multi-layer dominant reservoir superimposition method. Finally, well location optimization was carried out under the guidance of reasonable development countermeasures. As a result, better drilling effects are achieved.