Abstract: In this paper, The Lanzhou-Chengdu-Chongqing Products Pipeline is taken as an example to study the main factors influencing water carrying capacity of oil products and analyze the cause for internal corrosion of products pipelines. Fluent software is adopted to simulate the effect of flow rate, viscosity and updip angle of oil product on its water carrying capacity, and to analyze distribution of accumulated water during oil carrying water at sections with topographic relief or changed working condition parameters. Research is focused on the critical dip angles under different working conditions when Lanzhou-Chengdu-Chongqing Products Pipeline is in operation, so as to analyze its water accumulation situations and internal corrosion causes. It is indicated that water carrying capacity of oil products can be improved effectively by increasing flow rate and viscosity. Water tends to accumulate at the updip section with higher slope along products pipelines. A large amount of water accumulation at the low sections is the fundamental cause of internal corrosion of products pipelines.