A field experiment was conducted using the potato cultivar“Atlantic”as experimental material to study the potato root physiology and morphological development under 6 K levels［CK(0 g/plant),C1(1.2 g/plant),C2(2.4 g/plant),C3(3.6 g/plant),C4(4.8 g/plant),C5(6.0 g/plant)］,3 intensities of drought stress［D1(mild drought stress),D2(moderate drought stress)and normal irrigation］.Our experiment showed that,in the aspect of potato root physiology,the application of K fertilizer enhanced the drought resistance of potato root under drought stress.The root water content,root dry weight,root to shoot ratio were characterized by D1>D2 under different K level,all these indexes showed a significant difference under C3 treatment(P<0.05）except the root to shoot ratio,which showed nosignificant difference among 6 K levels.The producing rate of superoxide anion and MDA content were characterized by D2>D1 under different K level,the two indexes showed a significant reduction under C2 treatment(P<0.05）.The root vigor,CAT and SOD activity were characterized by D2>D1 under and below C1,C2 and C3 treatment,respectively,while the opposite trend under the higher K levels.POD activity showed a trend of D2>D1 under different K level on the whole.And these 4 indexes showed a significant difference under C2 treatment(P<0.05）.In the aspect of potato root morphological development,the total root length,root diameter,root surface area and root volume increased while the root tips decreased with the increase of K rates in a certain range.The root diameter,root surface area and root volume were characterized by D1>D2 under different K level,the total root length and root tips were characterized by D2>D1 under and below C2 and C3 treatment,respectively,while the opposite trend under the higher K levels.The response of root morphological indexes to the application of K fertilizer was complicated,it showed a trend of “mild droughthigh K level promote,moderate droughtlow K level promote”.In the aspect of potato yield,the tuber weight decreased under drought stress,while increased under different levels of K application,and showed a significant difference under C3 treatment(P<0.05）.To sum up,the application of K fertilizer should give full consideration to the local soil water condition on which to base the dosage,this would be beneficial to the improvement of the root resistance and the formation of the root morphology.