Based on breakthrough theory and fractal porous medium theory (FPM), the paper investigates the modelling mechanism of Ca(2+)removal in dicyandiamide by dynamic ion exchange. In this work, parameters within consideration included the flow rate of dicyandiamide crystallization mother liquor, the height-diameter ratio of the resin layer, and the temperature on Ca(2+)exchange. It was found that the removal efficiency of Ca(2+)reached 97.32%. Meanwhile, the through function of the process was obtained, and the behaviour of the dynamic process was modelled and simulated. In addition, using FPM theory, the calculation equation of the spectral dimension of the fractal surface of the resin in the ion exchange process was observed as linear and a mathematical model was established. This paper analyses the dynamics equation of the ideal surface and the fractal surface. According to the analytic results, it was linear relation on the ideal surface and power function on the fractal surface.