Abstract: [Objective] The DNA methylation, which is regulated by methylation and demethylation coordinately, directly affects the expression of stress-related genes.DNA demethylation in plants is mainly mediated by demethylase gene Ros1 (Repressor of silencing 1) to finish the base excision repair.Analysis of the dynamic changes of the DNA methylation of Halostachys caspica and gene expression changes of Ros1 will be helpful to elucidate the molecular mechanism of DNA methylation in response to salt stress.[Method]qRT-PCR was used to measure the degree of genomic DNA methylation in assimilation shoots and roots of H.caspica,the correlation between DNA methylation and HcRos1 gene expression was also analyzed.[Result]The results showed that the degree of genomic DNA methylation in assimilation shoots and roots of H.caspica increased firstly and then decreased under the same concentration of NaCl stress treated with different times, and DNA methylation in assimilating shoots was higher than in roots and reached the highest at 24 h.However,the degree of genomic DNA methylation in assimilation shoots and roots of H.caspica also increased firstly and then decreased under the different concentrations of NaCl stress treated with the same time, DNA methylation in assimilating shoots was higher than in roots and reached the highest under concentration of 100 mmol/L NaCl.The gene expression of HcRos1 did not changed under low concentration of NaCl stress, but increased significantly under concentration of 700 mmol/L at 72 h.[Conclusion]Correlation analysis demonstrated that the expression of HcRos1 was negatively correlated with the degree of DNA methylation.Salt stress can increase the expression of HcRos1, reduce the methylation degree of genomic DNA and enhance the salt tolerance of plants.