Abstract: In order to investigate the mechanism of how to control scale formation, a formula of resistance force to control scale formation process was proposed through analyzing the calcium sulphate scale over heated face. The higher velocity of slow and the lower super saturation, the more easily the surface reaction tends to dominate the whole process. The lower velocity and the higher super saturation, the more easily mass transfer tends to dominate the process, especially under the condition of higher temperature difference in liquid-wall and with high wall temperature. During the period of scale growth controlled by convection of mass transfer and surface reaction together, surface reaction would become to control the process only when the wall temperature were steady, but the control mechanism would last without change when the heat flux was constant.