Abstract: The pressure drawdown calculation method for conventional horizontal pipe now must be modified or expanded prior to being used for wellbore flow due to the differences between gas and liquid two -phase flow in horizontal wellbore and conventional horizontal pipes. In view of the effects of in-flow and out-flow of pipe wall on the pressure drawdown of annular fog flow, this paper presents a calculation method of pressure drawdown of gas and liquid two-phase annular fog flow with variable "mass in horizontal wellbores.