In recent years, many oil wells in Mahu oil fields have experienced scaling on the pipe wall, which leads to wellbore blockage and seriously affects the production effect. In this paper, the structure and composition of scale in Mahu oilfield were studied, and the mechanism of scale formation was investigated by using OLI?ScaleChem simulation method and the interaction experiments between fluid and rock matrix. The results show that the main fouling is CaCO₃, and the deeper the well is, the larger the amount of scale is. In addition, the wellbore temperature, pressure and pH of the fluid all have certain influence on scaling. According to the results of fluid rock reaction, it is inferred that CaCO₃ scale is the reaction product of highly mineralized fluid and calcium?rich minerals under the condition of acidic well fluid, and forms into balls under the action of polymer, resulting in hole and wellbore plugging. The results of the study are of great significance in guiding the proposal of subsequent scaling prevention and treatment measures in the oilfield.