Soil water characteristic curve (SWCC) is an important concept in unsaturated soil mechanics; and current research work requires SWCC to reflect more contents and factors. Among the factors influencing the SWCC, the influence from soil density is common and important. Research on how to mathematically describe the influence of soil density on SWCC is carried out. Based on the capillary model and Childs' (1950) statistical assumption, the motion law of the point on a SWCC in the situation of density variation is found; and an empirical method for estimating the SWCC corresponding to different initial soil densities based on two SWCCs with determined densities is proposed. Comparing the predicted results with experimental findings, a good precision is found. As the determination of SWCC from experiments is time consuming, predicting SWCC with different densities through this method can greatly reduce the workload of experiments, which can make the usage of SWCC in practice more convenient; besides, more influencing factors can also be considered.