Abstract: In this paper, we extracted the genomic DNA of Frankia from the nodules of Alnus nepalensis in Xishan mountain, Shishan mt.and Cangshan mt., and amplified the 16S rDNA of Frankia, then applied ARDRA(amplified Ribosomal Restriction Analysis)to study the influence of altitude an the genetic diversity of Frankia symbiozing with Alnus nepalensis. The results show that(1) The altitude is very important factor which can decided the genetic diversity of Frankia, (2)the higher the altitude gradient is, the more abundant the genetic diversity of Frankia, (3)some genotypes Frankia are restricted in a certain altitude height, and some appear in wide range of altitudinal height.