Topping can control the growth of main stem of cotton plant and avoid invalid fruit branches. The suitable time for topping is generally from early flowering to full flowering, and the specific time should be determined according to soil fertility, planting density, local best flowering and boll setting time and cotton plant growth. Those with low soil fertility, high density and few fruit branches should be planted early; Soils with rich fertility, low density and many fruit branches should be planted late. When topping, we should master the principle that "time is not equal to branches, and branches are not equal to time". If topping is too early, we can't make full use of the growing season, which will cause redundant buds. If it is too late, there will be many invalid fruit branches, which will consume a lot of nutrients and reduce the weight of bolls in the later stage. The topping method is generally to remove the main stem tip 1 leaf 1 heart of cotton plant.