Aiming at the over-size of lateral displacement of buttress No.3 and buttress No.12 in Meishan multiple arch dam, on the basis of observation data, the methods such as time-space analysis, numerical model, and structural calculation were applied to analyze the cause quantitatively from the topography and the structure of dam body.It can be concluded that the over-size of lateral displacement of buttress No.3 and buttress No.12 is the results of interaction of temperature load, the topography and the structure of dam body.