The water drive volume sweep coefficient is an important parameter in oilfield development. At present，its calculation method needs to fit the relative permeability curves of oil and water phases，and it is difficult to meet the application requirements of complex reservoirs with diverse oil-water percolation laws. To solve this problem，based on the approximate theoretical water drive curve and the Welge linear equation，a new dynamic calculation method of displacement efficiency and volume sweep coefficient of water drive reservoir is established through theoretical derivation. The volume sweep coefficient and displacement efficiency in different development stages can be calculated based on actual production data，which overcomes the dependence of existing methods on the relative permeability curves of oil and water phases. The results show that the new method is reliable，and can accurately obtain the variation rules of displacement efficiency and volume sweep coefficient in different water cut stages in complex reservoirs. The proposed method is featured with accessible date，convenient calculation，and wide adaptability to various types of reservoirs，and it can realize the accurate calculation from low water cut stage to ultra-high water cut stage，showing a broad application prospect in dynamic analysis and development effect evaluation in oilfield.