A high accuracy model to predict the amount of paper curl, which varies depending on the design parameters of fusing systems, is developed. To predict the curl, a visco-elasto-plasticity deformation model considering material properties under high temperature and moisture conditions in a fusing nip, and a dehumidification model considering the influence of decreasing drying were investigated. Proposed models were verified with two-roll fusing system and free belt nip fuser, and the models could predict the curl of different types of fusing systems under several conditions varying fusing temperature, moisture content of paper, paper type and amount of toner with high accuracy. This technology enables specification study of fusing and decurler systems without constructing many prototypes and, design man-hours needed for the development of a new system are reduced.