Abstract: Objective The project aims to study the effects of potassium uptake for nitrogen forms on different types of potassium efficiency genotype cotton under hydroponic condition.Method The study was conducted in the hope of finding out the effects of nitrate nitrogen and ammonium nitrogen on the cotton dry matter accumulation and potassium content,potassium accumulation,utilization index and root morphology under the condition of supplying sufficient potassium and inadequate potassium separately by choosing potassium efficiency genotype cotton of Liaomian 18,Jimian 958 and Xinmian 99B.Result The dry weight accumulation of root and stem,plant potassium content,accumulation and root morphology was increased by supplying sufficient potassium;Compared with nitrate nitrogen,ammonium nitrogen decreased dry matter accumulation,decreased potassium content and potassium accumulation,and hindered root development.Compared with Xinmian 99B,Liaoning cotton 18 and Jimian 958 in ammonium nitrogen treatment,dry matter accumulation,potassium content,potassium accumulation decreased less.Conclusion Compared with nitrate nitrogen,ammonium nitrogen is not conducive to cotton growth and potassium absorption,and potassium inefficient cotton varieties are more sensitive to ammonium nitrogen.