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