The present work aims to study the vegetation distribution and floristic composition according to the wadi system classification in Saint Cathrine Protectorate. The climate of the study area is extremely arid, with a long hot and rainless summer and mild winter. During the study, vegetation survey for the main wadis in southern Sinai was conducted, representing ecological variations such as elevation, physiographic characters, and soil conditions. Quantitative study of 317 stands in twenty-two wadis in southern Sinai, was done including; vegetation parameters such as total plant cover, physical and chemical soil analysis of the selected wadis. Temperature and moisture were the main factors controlling the floristic and structural distribution of vegetation in the study area. Species richness and diversity was highest in sub-sub basins and lowest in basins. Vegetation analysis in all wadis were classified into four groups; group (A) main-basin area included, Zilla spinose, Artemisia judaica, Hamada elegans and Anobasis articulata in five assemblages, group (B) basin area included   Artemisia judaica, group (C) sub-basin area included Alkanna orientalis and Artemisia judaica, finally group (D) sub-sub-basin area included Artemisia inculta, Alkanna orientalis and Artemisia judaica.  In conclusion, different wadi ranks had unique environmental conditions which controlled types and distribution of vegetation.