Abstract: Under conditions of circulating drilling fluid, the influence of dynamic head on the axial force of drill string can not be neglected. From fluid dynamics, the paper qualitatively and quantitatively analyzed the influence of dynamic head on drilling pressure during drilling deep wells. Lifting force is the important component of axial force of drill string. Engineering cases proved that lifting force influenced more axial force in deep wells. Therefore accurate calculation of lifting force induced by dynamic head of circulating drilling fluid has important significance for correct analysis of axial force of drill string and estimation of actual drilling pressure.