In order to investigate the gene structure, expression pattern, and molecular function of Kcna gene in Eriocheir sinensis, this study cloned the full-length Kcna gene of E.sinensis （named Es-Kcna）, and conducted bioinformatics analysis and spatio-temporal expression pattern research； observed the changes in growth phenotype characteristics of E.sinensis after RNA interfering with Es-Kcna gene； and screened the SNP molecular markers of Es-Kcna gene and conducted association analysis with population geographic distribution and growth characteristics. The results showed that Kcna gene was located on chromosome 46 of E.sinensis, with a length of 945,304 bp and nine exons. The full-length cDNA was 2 080 bp, the open reading frame was 1 584 bp, and encoded 527 amino acids, the total number of atoms is 8 433, the molecular structure formula is C₂₇₁₉H₄₂₁₀N₇₀₂O₇₈₇S₁₅, the predicted isoelectric point （pI） is 5.23, and the relative molecular weight is 59.81 KDa. Phylogenetic tree analysis showed that Es-Kcna gene was most closely related to the Kcna gene of Portunus trituberculatus, and the crustaceans clustered into a separate clade. Fluorescence quantitative PCR （qRT-PCR） results showed that Es-Kcna gene was expressed in six tissues, including muscle, heart, intestine, eyestalk, gill and hepatopancreas at pre-molting, inter-molting and post-molting stages, with the highest expression abundance identified in muscle tissue. Compared with the control group, the body weight, molting weight gain rate and second walking leg length of the experimental group crabs were significantly decreased after RNA interfering of the Kcna gene. Muscle tissue slice results showed that the diameter of muscle fibers in the walking legs of the experimental group was smaller than that of the control group. In addition, a SNP （A1 461G） was identified in the exon 8 of Es-Kcna gene. The association analysis of population distribution showed that this SNP was significantly enriched in the GG genotype in the wild population of Liaohe River, while the AA genotype was enriched in the wild population of Yangtze River. The association analysis of growth traits showed that the second walking leg length of individuals with the AA genotype was significantly longer than that of individuals with the GG genotype. The present study provided insight into the molecular function on Kcna gene in regulating growth and potential utilization in genetic breeding of E.sinensis, and provided an important reference for distinguishing wild E. sinensis from the Yangtze and Liaohe rivers.