Abstract: Providing a B3 transcription factor gene for simultaneously improving length, strength and elongation of cotton fibers. The cDNA sequence of gene GHFLS in tetraploid upland cotton TM-1 is SEQ ID NO. 1, and the genome sequence is SEQ ID NO. 2; GHFLS contains a non-synonymous mutation SNP, located at 1391 bp of the coding region with the base changing from A to G and the corresponding amino acid changing from Lys to Arg. The GHFLS gene was overexpressed in Arabidopsis thaliana caused a significant reduction in the root length of the T2 generation, demonstrating its important role in the cell elongation mechanism. The fiber quality of the cotton variety (line) with haplotype AA is significantly better than that with haplotype GG. The gene has important research value and application prospect in efficiently identifying high-quality fiber upland cotton varieties, improving cotton fiber quality and cultivating new varieties of high-quality cotton fibers.