Various non-chemical water treatment methods have been utilized to solve fouling problems. All of these methods have never been scientifically proven to be a valid tool for controlling scales, and one of reasons could be the lack of understanding of the operational principle and treatment mechanisms. The present study focuses on characteristics of calcium carbonate crystal size distribution in solution and crystal structure on the surface under the electromagnetic field in order to comprehend the mechanisms of the Electromagnetic treatment device (ETD). An electromagnetic treatment setup was built for treating scaling water, and a series of fouling tests were carried out with and without ETD, analyzing the particles size distribution in solution by Dynamics Light Scattering (DLS) technology and making Scanning Electron Microscope (SEM) photos. The main results were as follows：The number of precipitate nucleation in solution was few and the particle growth was slow without ETD. In opposition to the case untreated, a rapid particle growth was observed and the number of nucleation was expected to be more, due to the ETD effectively increasing the ions and crystals collision frequency and effectiveness by utilizing the induced electric field. It was implied that the particle growth was promoted mainly by coagulation process but not nucleation growth in all the experimental temperature range. In the high temperature, the crystal phase of calcium carbonate could be changed from aragonite type without ETD to calcite with ETD. In the lower temperature, all the precipitated crystals in solution were calcite and there were little differences between with ETD and without ETD.