Tong Xianzhang’s chart plate relation curve is a statistical regularity summarized by medium and high permeability reservoirs at home and abroad and it cannot objectively reflect actual characteristics of a particular reservoir. Large deviation exists between the actual value and theory value obtained from evaluation of reservoir water content and recovery degree by using Tong Xianzhang ' s chart plate. According to static characteristic parameters, permeability rule and dynamic moisture content change of water flooding reservoir, applied is the water flooding characteristic curve to analyze the constant 7.5 in Tong Xianzhang’s chart plate relation curve formula for moisture content evaluation and derived is the relational expression instead of the constant. Actual application shows that the improved chart plate can reflect actual reservoir moisture content change in an even better fashion and has strong application value.