Abstract: A single sine model is developed that calculates the accumulated degree-days(DD） of cotton development stages,the change rule of cotton phenology in1980~1999years is done by the cluster analysis with complete linkage method(CLM）,simultaneously,the regression model between cotton yields and degree-days is realized.The result shows approximately 53.18,109.99,360.97,635.64,1169.61and 1180.02DD are the requirement degree-days for seed,seedlings,showing bud,flower,splitting boll,opening boll,and stopping growth,respectively.The accumulated degree-days of cotton growth are varied in 4~5years periodicity.In early cotton stages,seed and seedlings stages,variability of degree-days is bigger than that of other cotton stages,Coefficient of variations are44.1and30.4percent in seed and seedling stages.Four type,cool,warm, hotter and hottest year,is clustered via CLM.Cotton yields(y） and accumulated degree-day for whole year (x1）,stopping growth period(x2） and post-september(x3） is correlated positively.The regression equations is y =–2101.75+2.379x1,y =–2169.35+2.446x2 and y =167.70+7.339x3,respectively.In hotter and hottest years,cotton yields are higher than that of cool and warm years.To apply sums of degree-days of cotton stages and manage cotton growth and production,it is better than calendar time.

Key words: Cotton, Phenology, degree-day, cluster analysis, the northern of Xinjiang