Abstract: To explore the role of the Venation sequence characteristic of Citrus plants it plays in plant classification and biological evolution; 4 citrus plants venations were compared with light microscope. Leaf venations of Citrus reticulata,Citrus grandis,Citrus limon and Citrus sinensis are brochidodromous. Primary vein radiates in a straight or a slightly curved direction. The venations are of a quinternary vein and veinlets have 0 or 1 ~ 2 branches. Leaf margin is of a tertiary vein ring. Leaf venation characteristics of Citrus reticulata,Citrus grandis,Citrus limon,Citrus sinensis are basically the same. The intersecondary veins, tertiary vein, the development of areole, in particular, the characteristics of veinlets branches showed a high degree of stability, with only a slight variation detected in the number of secondary veins and development angle. Leaves from different parts of the same species are just identifcal. The above - findings in vein characters support that Citrus reticulata,Citrus grandis,Citrus limon,Citrus sinensis are in similar evolutionary status. They belong to sibling species. Therefore, the characteristic of the Citrus leaf venation is one with relatively conservative feature. It can serve as a basis for plant classification.