Abstract: To control the proper cotton planting density and field microclimate, Xinluzao No.45 cotton was taken as the experimental variety to design 5 different densities, and the temperature at different levels of population, relative air humidity, light transmittance and illumination intensity as well as the agronomic traits of the cotton in the harvest time were measured when the max canopy density in the later period of cotton efflorescence. The results showed that there was little difference in temperature among populations with different densities, while the difference of gradient temperature among plants was significant. The proper gradient temperature difference suitable for cotton populations was less than 0.4 ℃. The relative air humidity with high density treatment （270 000 plants/hm²） among populations were 3 percentage point higher than that with low density treatment（90 000 plants/hm²）. In order to achieve high yield, the ground light transmittance among cotton plants should be more than 5.5%. The planting density of cotton had significant negative correlation with the plant height, stem diameter, single boll number and weight. Under the current cultivation and management level, the planting density of northern Xinjiang early-maturing cotton variety should be 180 000~220 000 plants/hm².

Key words: cotton, density, microclimate, output