针对直井钻进过程中环空内岩屑运移的特点，对环空中固液两相流动压降进行了理论分析。采用因次分析的方法综合考虑了影响压降的诸多因素，导出了固相摩阻系数与傅劳德数之间的关系，提出了总摩阻系数的理论计算公式，修正了过去计算环空压降时忽略固相引起的压降，为准确进行水力优化设计提供了参考依据。 Aiming at the characteristics of debris flow in annulus during vertical well drilling, the pressure drop of solid-liquid two-phase flow in annulus is theoretically analyzed. The factors affecting the pressure drop were comprehensively considered by the method of factorial analysis. The relationship between the solid friction coefficient and the Froude number was deduced. The theoretical formula of the total friction coefficient was proposed, Neglecting the pressure drop caused by the solid phase when pressure drop, it provides a reference for accurate hydraulic optimization design.