An electromagnetic anti-fouling (EAF) device was built for treating scale containing water. In order to validate the effect and identify the mechanisms of EAF technology, a series of experiments were carried out, both with and without, an EAF device. The fouling thermal resistance was measured as a function of time. Scanning electron microscope (SEM) images of the fouling layers were obtained and the particle size distribution in solution was analyzed by dynamic light scattering (DLS) technology. The main results were as follows: (1) With EAF treatment, the crystal phase of calcium carbonate was changed to calcite from the aragonite type which exists without EAF treatment; (2) A rapid particle growth was observed under EAF treatment conditions. This rapid growth was due to that the EAF treatment results in all induced electric field inside the bulk flow, and can effectively increase collision frequency of the ions and crystals along with the effectiveness of collision. This implies that the particle growth was promoted mainly by a coagulation process, and not by nucleation growth; (3) The EAF treatment greatly reduced the fouling resistance within the time period tested.