Population genetic structure and genetic diversity were studied using RAPD in five samples of Petrosimonia sibirica in Fukang, XinJiang. The results showed that amplification of 14 random primers detected 76 of 77 loci were polymorphic. The mean proportion of ploymorphic loci (P) of P. sibirica was 98.7%. It showed the higher genetic diversity existed in the subpopulations of P. sibirica. Furthermore, the study discussed the Shannon information index (HPOP/HSP =0.6933), Nei gene diversity index (HS/HT=0.6948) and gene differentiation index (GST=0.3052). The analysis presented that the ratio of molecular variation was over 30% among subpopulations and about 70% within subpopulations. Therefore the genetic differentiation had happened among subpopulations of P. sibirica. On the other hand, the gene flow of P. sibirica (Nm=1.138) was less than that of cosmopolite species (Nm=1.881), and much lower than that of of Caragana spp. populations over Maowusu sandy grassland (Nm=5.9529). Additionally, through the correlation analysis, the relationship between the genetic distance of P. sibirica and latitude, longitude and altitude was not significant. It showed the geographical difference was not one of the potential factors, which affected the genetic differentiation of P. sibirica. At the same time, the soluble salt in soil of the oasis desert transitional zone might play a role in maintaining the genetic diversity of P. sibirica. The paper indicated that the mean proportion of ploymorphic loci (P)and Nei gene diversity index (H) of P. sibirica had the remarkably negative relationship (p<0.05) with the total K and Cl- in soil respectively. Above analysis showed that although much of genetic variation existed within the subpopulations, the genetic differentiation occurred among subpopulations. The natural selection may have a determinate effect on keeping the genetic variation and differentiation of the subpopulations of P. sibirica.