Abstract: [Objective] The project aims to explore the interaction effect of chemical topping and water on cotton,the effects of different drip irrigation amount on canopy structure,dry matter distribution and yield of the chemical topping cotton in order to provide theoretical basis for chemical topping technology.[Method] Under the natural conditions in the field,the artificial topping was used as the control,and two topping agents,the combination of fluorine amine compound and DPC,were selected.After applying the topping agent,two drip irrigation (routine irrigation),middle drop water quantity (85; normal irrigation volume) and low drop water quantity (70; regular irrigation amount) were set up and after that,3 different water drop amount were applied.The leaf area index of different cottons were determined in different parts of the canopy light transmittance,dry matter accumulation and yield components in different conditions;The canopy characteristics,light distribution,material allocation and yield change of chemical topping cotton were analyzed under different drip irrigation conditions.[Result] Chemical topping cottons had the high leaf area index (LAI) and the longest duration,under middle drip irrigation which led to the increase of the photosynthetic area,and the appropriate DIFN,light distribution and canopy structure were beneficial to increase the light efficiency.The higher dry matter improved proportion percentage of photosynthetic material to reproductive organs.The lower drip irrigation amount also decreased the cost compared with the high drip irrigation.And the middle drip irrigation amount treatment significantly increased seed cotton yield compared to the low drip irrigation amount treatment.[Conclusion]Therefore,the two irrigation should be controlled in middle drip volume (32m3/667 m2) after spraying topping agent,which can not only optimize chemical topping cotton canopy structure,but also promote photosynthetic material to the reproductive organ allocation and give full play to water-saving irrigation under mulch,and increase the efficiency and productivity.