Abstract: Morphological observation and gene mapping were used to investigate the growth and development mechanism of stem and molecular mechanism of dwarf-slim stem formation in Phaseolus vulgaris L. variety A18 and dwarf slim-stem mutant nts,in order to locate the purpose gene.The results showed that the plant height, main stem thickness, top stem thickness, number of branches, number of nodes, and 100-grains weight of nts were significantly lower than those of wild type; the net photosynthetic rate, stomatal conductance of leaf and transpiration rate of the mutant were lower than those of the wild type, and the intercellular CO₂ concentration was higher than that of the wild type.As the plant grew, the antioxidant enzyme activities of nts,SOD,POD,and CAT were all reduced compared to the wild type, and the ■ content increased compared to the wild type.Genetic analysis showed that the gene was inherited in a recessive single gene, and it was initially located between SSR markers SSR47 and SSR65 on chromosome 8.The physical distance was 574 kb, and there were 67 annotated genes in this interval.