This study reviewed data from 1950 to 2014 on 1,257 upland cotton (Gossypium hirsutum L.) cultivars from three agroecological regions in China: Yellow River Valley, Yangtze River Valley, and Northwest Inland. The main aim was to establish future breeding and cultivation strategies. Lint yields significantly increased linearly in the three regions over time. Yield improvement in the new cultivars was due to: the decrease in planting density and increase in lint percentage and single boll mass in Yellow River Valley, the decrease in planting density and increase in lint percentage and bolls per plant in Yangtze River Valley, and the increase in planting density and lint percentage and decrease in bolls per plant in Northwest Inland. Planting density had significant effects on bolls per plant, single boll weight, lint percentage, growing period, and plant height in the three ecological regions. Our results suggest that different regions require different breeding strategies, and the evaluation of the genetic improvement process of cotton should not ignore the effects of planting density.