| 35 soil samples were collected from the region of northern alp of Hengduan Mountains of Qinghai-Xizang Plateau. The soil actinomycetes were separated and identified. According to the quantities and the communities, the relationships between them and some environment factors were analyzed, respectively. The actinomycetes diversity was also studied. Potential which could antagonize to pathogen and the differences in different fermentation condition were also analyzed.The results showed that the quantity of actinomycetes was about 2.46×105±2.86×105 in upper (0～20cm). At the same plot, there were more actinomycetes in upper than in deeper soil layers.Quantities of actinomycetes from high to low were as follows: in different regions, Zheduo Mountain(5.05×104 cfu·g-1dry soil)＞Songlinkou(2.34×104 cfu·g-1dry soil)＞Que'er Mountain(1.17×104 cfu·g-1dry soil). In different soil textures, clay loam(2.91×105cfu·g-1dry soil)＞loam soil(2.87×105 cfu·g-1dry soil)＞sand loam(2.15×105 cfu·g-1dry soil)＞powder sandy loam (1.98×105 cfu·g-1dry soil)＞heavy clayey soil (1.71×105 cfu·g-1dry soil); In different land utilization way, forest land(3.25×105 cfu·g-1dry soil)＞grass land(2.27×105 cfu·g-1dry soil)＞brush forest land(1.28×105 cfu·g-1)dry soil). Quantities of actinomycetes were changed with altitude, but the degree of the impact is not great. At the same plot, there were more actinomycetes in upper (0～20cm) than in deepersoil layers (20～40cm).Based on characteristics of morphology, physiology-biochemistry and 16S rDNA sequence, 5 genera were identified among these isolates. These genera included Streptomyces, Streptosporangium, Nocardia, Ampulariella and Micropolyspora. Among these genera, Streptomyces was the first, Streptosporangium and Nocardia were next, and Ampulariella and Micropolyspora were the least. As far as quantity was concerned, Streptomyces was also the most, its value was 1.27×105 cfu·g-1dry soil and its separation frequency was 100%. Moreover, the Streptomyces included Griseofuscus, Albosporus, Aureus, Globisporus, Roseosporus, Verticillatus, Griseorubroviolaceus and Lavendulae. Among these, Griseofuscus and Albosporus were domination, and their separation frequencies were 92.59% and 85.19%, respectively. There were 4 genera in loam soil and sand loam, 3 genera in clay loam and powder sandy loam, 4 genera in forest land and grass land, and 2 genera in Brush forest land, respectively. At the same plot, Quantity of actinomycetes genera in upper (0～20cm) was more than these in deepersoil layers (20～40cm).The abundance(S), Shannon-wiener's diversity (H'), Pielou's evenness (E) and dominance index (D) of the quantity of actinomycetes were different. Their values were 2.0000±0.7845, 0.1124±0.0359, 0.0698±0.0223, 0.0006±0.0004, respectively. And the abundance (S), Shannon-wiener's diversity (H'), Pielou's evenness (E) and dominance index(D) of Streptomyces were 4.3333±1.0742, 0.1313±0.0427, 0.0631±0.0206, 0.0003±0.0002, respectively.Among 258 isolates, there were 97 isolates had obvious antagonistic effects against Rhizoctonia solani and 11 isolates had obvious antagonistic effects against Sclerotium rolfsii. 83.51% and 81.82% of antimicrobial actinomycetes which had antimicrobial activity against the two plant pathogens were Streptornyces, respectively. And there were 81 isolates against Rhizoctonia solani, 9 isolates against Sclerotium rolfsii. Strain 14-17 had their strong inhibition activity with fermentation 6 days, the initative pH of 7～8, 28℃～32℃tempereature and the vibration raises. Whereas 8-16 with fermentation 8d, pH of 7, 28℃tempereature and the vibration raises. Wherase 16-15 with fermentation 8d or 4d, pH of 7～8, 28℃tempereature and the vibration raises.
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