This study surveyed floristic composition and distribution of weed vegetation in Mituo County. 206 relevés were surveyed according to relevé method. A total of 140 species belonging to 32 families of the vascular plants were recorded. The weed communities were classified with nonmetric multidimentional scaling, two-way indicator species analysis, tabular comparison method, fidelity and synoptic table analysis. Discriminate analysis was used to evaluate the distinctness of classification unitsal vegetation classification system was made using Braun-Blanquet approach of floristic-sociological classification in lower levels and physiognomic-sociological classification in higher levels. In floristic-sociological classification, assication is the basic unit, and it should be grouped into higher units (alliance) by floristic composition. The results showed 1 formation class, 2 formations in phsiogonomic units, and 4 alliances, 6 associations in floristic units: I. Lower montane-lowland weed vegetation formation A. Echinochloa colona alliance a. Echinochloa colona association b. Trianthemum portulacastrum association c. Panicum maximum association B. Dichanthium aristatum alliance d. Dichanthium aristatum association C. Eriochloa procera alliance e. Eriochloa procera association II. Sand dune vegetation formation D. Ipomoea pescaprae subsp. brasiliensis alliance f. Ipomoea pescaprae subsp. brasiliensis association