In order to control the thermal expansion coefficient of leucite effectively,the leucite powders were remodeled by cesium ion. The leucite powders were treated by hydrothermal ion exchange in 0.3 mol/L cesium sulfate solution.The phase composition and morphology of the samples obtained at 180 ℃ for different ion exchange time were analyzed and observed by X-ray diffraction（XRD） and scanning electron microscopy （SEM）.Results showed that the cesium ions introduced crystal lattice of leucite can make conversion of partial leucite into pollucite.The pollucite crystals gradually transited from the tetragonal system to the cubic system with the increasing of the holding time.When the holding time exceeded 10 h,the in-creasing of internal stress between two phases leaded to pollucite falling off from the surface of leucite grains,so the holding time should be controlled at 2~10 h.The fitting analysis of the kinetics of the synthetic pollucite using the JMA equation showed that the Avrami exponent n of the hydrothermal ion exchange reaction was less than 0.5.That indicates that the reac-tion was dominated by diffusion.