Abstract: In order to select sea island cotton varieties of high oil content and the most optimal flowering stage, the change characteristics of physical traits and oil traits as well as the relationship between them were analyzed by taking cotton seed of 20 sea island cotton varieties of Xinjiang of China, Egypt, America and Central Asia at 8 flowering stages as test materials by using biological statistics and Soxhlet extraction method. Seed oil index and kernel oil index of sea island cotton had significant genetic variability, and their variable coefficients were 12.86%. Cotton seed oil traits of XH-36, XH-41, DJC-3, DJC-4, DJC-5 and A-Za were significantly higher than that of other varieties, and the optimal oil traits of these six varieties was on July 5^th, followed by June 30^th and July 20^th. Therefore, six high quality varieties of sea island cotton were screened out initially through the test. Moreover, the correlation analysis showed that there was interaction between physical traits and oil traits of cotton seed, which could affect cotton seed quality jointly, and cotton seed oil traits were regulated by its physical traits.