Abstract: A new dilatancy equation is proposed by adding a factor to the dilatancy equation of Cambridge model, and this factor can adjust the shape of curve between the dilatancy ratio and the stress ratio for coarse-grained soils, and can reflect the nonlinear relationship. Thus a new constitutive model based on the generalized plastic theory is proposed. The main conclusions are as follows: (1) The method of determining the parameters of the proposed dilatancy equation is simple, and its capability to reflect the dilatancy properties of coarse-grained soils is verified by CD tests; (2) There are 9 parameters in this model and their definitions are clear, and the methods to determine parameters through the indoor tests are given; (3) According to the generalized plastic constitutive model, the stiffness matrix under the general stress state is deduced, and the triaxial constant p tests and two-stage constant-stress-ratio tests are carried out to verify its rationality.