Size segregation is one of important properties of vibrating granular matters. It is significant to understand and study the segregation mechanisms and parameter range of controlling factors of mixed granular matters for the development of industry, agriculture and pharmaceutical. In this paper, we investigate the influence factors and physical mechanisms of "Brazil Nut" segregation experimentally and theoretically. The influences of vibrating acceleration, sizes and densities of large and small granules on the segregation time are analyzed. The hydro-model is used to evaluate segregation time and explain the experimental results qualitatively. Results show that the vibration acceleration is a main controlling factor for "Brazil Nut" segregation in the case of fixed frequency. There is a critical acceleration. When the acceleration is larger then its critical value the main physical mechanism changes from convection to filling voids, and the effect of acceleration on segregation decreases, while the effect of size of large granule on it increases. Furthermore, "Brazil Nut" segregation still arises when the density ratio is equal to 1. The increase of the size or density of small granular may enhance "Brazil Nut" segregation.