Abstract: To study the deposition characteristics and mechanism of composite fouling of MgO particles and calcium carbonate on the heat transfer surface, a molecular dynamics method is adopted to investigate the deposition process of MgO particles and calcium carbonate composite fouling on copper heat transfer surface, and the influence of calcium carbonate concentration on the deposition characteristics of composite fouling is discussed. The results show that in the process of composite fouling deposition, calcium carbonate clusters play a connecting role between the particles and the heat transfer surface, forming a stable deposition state. In addition, MgO particles have an effect on the kinetic and structural characteristics of the formation of clusters by ion association. As the concentration of calcium carbonate increases from 0.26mol/L to 1.1mol/L, the number of calcium carbonate clusters directly adsorbed on the heat transfer surface increases, and MgO particles are easier to deposit on the heat transfer surface through the interaction of calcium carbonate clusters. MgO particles promote the process of calcium carbonate aggregation, and calcium carbonate promotes the deposition of mixed clusters, which form the initial stage of composite fouling deposition.