Abstract: The recorded number of the seed plants (besides planting)found in Lujiangba dry-hot valley which is below 1300 m amount to 361 species belonging to 259 genera of 81 families. Among them, Enteropogon is found in Yunnan for the first time. The flora, which has 51.5 tropical and subtropical families and 77.6 tropical genera, is obviously a tropical one, and it has close connection with the flora of pantropic, old world tropics, tropical Asia and tropical America.It means that the origin and connection with other tropical flora is quite ancient, re-flecting the relict background of Gondwana flora. The distribution of ?4 Gramineae plant has some links with climate, in this paper the writer points out that the number of this kind of plants can be used as one of the index to reflect the environmental dryness and hotness.

Key words: Dry-hot valley