Abstract:According to the method of the French--Swiss phytosociological school, and through the test of principal componcnt analysis, a systcmatical resc-arch on the vegetation of the dry-hot riyer valley in Yuanmou has been underta- ken, in which the main associations and their units have been accepted as follows: Ass. I Hcteropogonetum contorti,Subass. 1 bothriochloetosum,Fac. (1 ) Rumex hastatus Subass. 2 cymbopogonetosum ,Ass. E Hyparrhenietum eberhardtii,Ass. III Bothriochloetum pertusae