At a time when China is undergoing a shift in economic growth rate, how to have a good grasp of the extent to which the potential economic growth rate will slow down is a grand issue in macro-control. This paper focuses on three important topics in macro-control in recent times: "proceeding actively with reform and restructuring while stabilizing economic growth", "rational range", "medium-to-high speed economic growth" and the paper makes relevant quantitative analyses. This paper finally puts forward policy suggestions regarding macro-control: it's better for the authorities to grasp the "midline" rather than keep within the "lower limit". <<