Gravity load case is generally the control condition of the reinforcement design of high arch dam. Because of the particularity and complexity of the construction process of high arch dam, there are several ways to apply gravity load, such as joint deadweight and whole deadweight. In this paper, the influence of gravity applying approach on corridor stress and reinforcement of high arch dam is studied through three-dimensional finite element analysis. Results show that in whole deadweight case, the stress and reinforcement area of the corridor structure are apparently small; while in joint deadweight case, the stress and reinforcement area of the corridor structure of are obviously larger than those of the deadweight results according to construction process. According to the actual construction process and the bearing capacity law of the structure, gravity load should be considered in the construction process in finite element calculation of arch dam to ensure structural safety and economic rationality. The research achievements could be taken as reference for the design of overflow outlet structure.