Abstract: The field experiments on the effects of 3 planting densities on the canopy apparent photosynthesis, canopy structure and yield of cotton drip-irrigated under the mulch were conducted in earlier harvest area of North Xinjiang. The results indicate that the optimum population density of the cotton is 240000 plantlets/hm², under which the canopy structure, canopy apparent photosynthesis, leaf index, dry matter accumulation and distribution and lint yield of cotton are better than those under other densities.