A kinetic model for the adsorption desorption of ammonia on SCR catalyst with single or dual active sites weas established. To this end， the model parameters were identified by ammonia adsorption desorption tests on powdered SCR catalyst. The experimental results show that the adsorption desorption process of ammonia on SCR catalyst can be described by the dual active sites reaction kinetic model than the single active site reaction kinetic model. The influences of temperature and ammonia inlet concentration on the ammonia storage capacity of SCR catalyst were studied based on the dual active sites reaction kinetic model. The simulation results show that the higher the temperature， the less the ammonia storage capacity of SCR catalyst， and the higher the ammonia inlet concentration， the higher the ammonia storage capacity with weak adsorption site， while the ammonia storage capacity with strong adsorption site remains the same.