The effect of potassium application on stem lodging resistance of Japonica rice in cold region was investigated using Dongnong 425,Dongnong 427 and Songjing 6 as experimental materials.The results showed that under appropriate potassium application,plant height increased,center of gravity height moved up,the length of the first and second basal internode became short,the third basal internode length became long,stem coarseness and plumpness increased,stem wall became thick,flexural strength and bending moments increased,lodging index decreased,lodging resistance capacity strengthened,stem and sheath total soluble sugars content increased,rice actual yield improved.The flexural strength of each internode had a very significant positive correlation with stem coarseness,plumpness,stem wall thickness,total soluble sugar content of stem and sheath,whereas it had no significant correlation with plant height,center of gravity height and the yield.The flexural strength of the first and second internode showed a very significant negative correlation with the internode length,and the flexural strength of the third internode had no significant correlation with its length.The lodging resistance of Dongnong 425 and Dongnong 427 were best under the treatment of 75 kg/hm2 K2O rate,while the lodging resistance of Songjing 6 performed best under the treatment of 100 kg /hm2 K2O rate.