The invention discloses a late-dense-simplified cotton cultivation method adopting chemical topping. The late-dense-simplified cotton cultivation method comprises the following steps of sowing in the first ten-day period of May, performing final singling at a 2-3-leaf stage, and controlling the density of reserved seedlings at 5,500 to 6,000 plants/mu; then spraying a chemical topping agent for three times: at the first time, spraying when 60 percent of plants in a cotton field reach 9 to 10 fruit branches, and spraying to tips of leaf branches and fruit branches by using a mixed liquid of mepiquat chloride and flumetralin according to the ratio of 2:1, at the second time, spraying when 60 percent of cotton plants in the cotton field reach 10 to 11 fruit branches, and spraying to top ends of cotton plant stems by using a mixed liquid of the mepiquat chloride and the flumetralin according to the ratio of 1:2; at the third time, spraying at the sixth to eighth day after second spraying, and spraying to whole plants by using a mixed liquid formed by adding the mepiquat chloride and flumetralin according to the ratio of 1:1, and 0.05 percent of urea. According to the late-dense-simplified cotton cultivation method disclosed by the invention, rotten bolls are reduced and premature senescence is alleviated by proper late sowing; density increasement and chemical topping are used to replace artificial pruning and topping, so that labor and time are saved, and net incomes are remarkably increased.