Abstract: Salt stress is one of the major factors reducing crop yield.In this study,an Arabidopsis salt-sensitive mutant EMS85 was obtained by ethyl methane sulphonate (EMS) mutagenesis strategy.Genetic analysis indicated that salt-sensitive phenotype was controlled by a single recessive locus.Using map-based cloning technique,24 pairs of SSLP markers were picked up which evenly distributed on the 5 chromosomes as the coarse mapping, and a series of molecular markers were designed through the fine mapping.Through coarse mapping and fine mapping,EMS85 has been mapped to a region between molecular marker LUGSSLP847 and 5-13.58 on the chromosome V.The mutant was proved to be an allelic mutant of SOS2 gene by sequencing and blasting, mutational site carried a two deletion in the 1521—1522 bp of SOS2 gene,which caused frameshift mutation and functional incapacitation of SOS2 gene.The map-based cloning technique has greatly accelerated the process of gene cloning,it takes half a year in localizing the EMS85mutant, which could determinate a candidate gene quickly for other mutants and accelerate the gene mapping process.