Abstract: Under the climatic conditions in Shandong Province, cotton growth and development are mainly restricted by heat conditions. By means of phenological stages of cotton fields calculated by accumulated temperature for cotton growth areas with different state of climatic ecology, different varieties, planting ways, density and yield levels of crop, the suitable chemical controlling stages are determined, which could change the microclimate of cotton fields, raise 10%~15% of mature boll and 0.3~0.9 g of one boll weight, and change seeding time and varieties because of shorter button stage, expand areas of double cropping with wheat and cotton, and improve cotton quality