Abstract: Experiment was conducted to study potassium efficiency and its mechanisms of different cotton genotypes.Six different Kefficiency cotton genotypes (code: 103,122,138,163,165 and 169),were selected as experimental materials from 86 cultivars for 2 years.The research started from May 14,2003,and accomplished on June 12 using HCАВДОНИН ingredient water culture with two K levels and three repetitions.Firstly,dipped cotton seeds into 5060℃ water for 30 minutes,then preserved seeds in doors at normal temperature.When bud emerged,bed them out in the solution pot.The volume of plastic pot bulk is 20 L. For each pot 12 plants was planted and was placed on the Lab terrace.Oxygen was add to the solution about 10 hours everyday using machine.The nutrient solution was refreshed once a week to prevent and cure plant illness and worms.Plant height and leaf number were record.Finally roots,stems and leaves were harvested separately.Oven dry them at 105℃ for 30 minutes,then at 70℃ for 24 hours. The results indicated that KEC K efficiency coefficients and YP(yield potentiality) were different.KEC of those six genotypes were 0.30,0.22,0.34,0.36,0.38 and 0.24,and GP were 2.46,2.21,1.83,1.27,1.46 and 1.49,respectively.Base on the variation of KEC and GP,different could be classified into four group: High KEC with high YP(103 and 138);high KEC with low YP(163 and 165);high YP with low KEC(122) and low KEC with low YP(169).Under K stress condition,103 and 138 grew much better than other genotypes,with the biggest dry matter,while their K content was the lowest,which indicated that they could made up more dry matter under K stress,therefore they had a higher KEC.Besides,the ratio of shoot and root was much larger for 103 and 138 than other genotypes,which indicated that less root matter was used to maintain more shoot growth.As the results,they had higher K cumulant in plant and the ratio of K cumulant of shoot was bigger.There was an obvious difference in K absorption,transportation,distribution and utilization among different genotypes.K cumulant of 103 and 138 was the highest whenever under+K or-K condition,and the K cumulant showed a distinct variation among these six genotypes under-K condition,while under +K condition,this variation diminished.Up-leaf chlorophyll content of 103 and 138 was much higher than that of down-leaf.By contrast,genotype 122 and 169 had high K content with the lowest dry matter,among which the dry matter of 169 was only accounted for 43.93% of 103.Therefore their K absorption,accumulation and utilization abilities were rather weak.K absorption,accumulation and utilization abilities 163 and 165 were medium.