In present study, we develop a new segregation index having both geometrical and physical significances, on the basis of segregation profile of granular bed. We carry out a DEM simulation to validate this index and analyze the segregation of binary mixture. The DEM analysis reveals that the segregation profile of granular bed subjected to vibration is in general in a reverse “N” mode, which tends to narrow and weaken as vibration continues. At a proper vibration amplitude, the reverse “N” pattern diminishes progressively and the overall segregation profile evolves into a three-line-segment pattern which stands for the ideal state of full segregation. A comparison analysis indicates that the new index proposed in this study is able to give a more proper estimation of segregation phenomenon for binary mixtures, as compared with other indices from the literature.