Diverse genetic variation is of great importance for crop ecological adaption and genetic improvement.In order to know the genetic diversity of early maturity in upland cotton, 186 upland cotton (96 early-maturity and 90 later-maturity upland cotton) were explored using136 simple sequence repeat (SSR) markers, and a total of 355 distinctive loci were detected with an average of 2.61. A total of 341 distinctive loci were amplified from 134 SSRs with an average of 2.54 per SSR in early-maturity upland cotton and 345 distinctive loci were amplified from 133 SSRs with an average of 2.59 per SSR in later-maturity upland cotton. Mean polymorphism information content (PIC), average effective numbers of alleles (Ne) and average genotype diversity index (H′) were 0.684, 3.994 and 1.361 in early-maturity upland cotton, and 0.668, 3.852 and 1.343 in later-maturity upland cotton, respectively. The similarity coefficients were similar between early-maturity upland cotton and later-maturity upland cotton, ranging from 0.349 to 0.935 in early-maturity upland cotton with an average of 0.635, and ranged from 0.270 to 0.907 in later-maturity upland cotton with an average of 0.666, respectively. These varieties were clustered into two groups using unweighted pair group method analysis (UPGMA). The high genetic similarity coefficients of the early-maturity upland cotton indicated the genetic background of early-maturity upland cotton was narrow in China. These results are useful for assessing cotton pedigrees, improving cotton hybrids, and ultimately allowing for the improved utilization of early-maturity cotton.