Objective Genetic diversity and affinity relationships among 13 species of Dendrobium Sw.were analyzed,the result laid a solid foundation for the better use of this resources.Methods Random amplified polymorphic DNA(RAPD) technique was used to analyze genetic diversity,and the dendrogram was constructed by UPGMA.Results Ten RAPD primers were applied to do random amplification.A total of 188 DNA bands was detected,180 among which were polymorphic,the average rate of polymorphic bands was 95.74%.The result of cluster analysis by using UPGMA method showed that 13 genotypes could be classified into three types in genetic distance 0.63.This outcome was corresponding to the result by using traditional classification.Conclusion It is concluded that RAPD markers can be used on the studies of genetic relationships and classification of species of Dendrobium Sw.sensitively.