Abstract: At present, shut-in pressure is the main factor that is taken into consideration when the casing setting depth is designed.In the actual process of well killing, however, the peak annulus pressure during the circulating out of the gas is higher than the annulus pressure during well shut-in. To prevent circulation loss in the whole process of overflow well control and reduce the effect of formation pressure uncertainty on well control risk, the peak annulus pressure was calculated by calculating the change of annulus pressure during the circulating of the overflow materials out of the borehole by means of circulative well killing, and the chart for the variation of peak annulus pressure with the overflow strength was established. Besides, it was proposed to determine the casing setting depth according to the peak overflow annulus pressure, combined with the formation fracture pressure. It is proved from the case calculation of an oilfield that this method can define the kick strength corresponding to the casing setting depth, and thus the uncertainty of formation pressure is the controllable and the casing setting depth is designed precisely.