Abstract: To investigate effects of different potassium application levels on maize grain filling characteristics and yield, field experiments were conducted under typical area of north China plain, using summer maize "Zhengdan 958" as experiment material．Five treatments were established including no potassium（K₀ treatment）, low potassium（K₁ treatment, 90 kg/hm²）, medium potassium（K₂ treatment, 180 kg/hm²）, high potassium（K₃ treatment, 270 kg/hm²）, and ultra-high potassium（K₄ treatment, 360 kg/hm²）．Maize grain filling process, filling characteristics（maximal filling rate, average filling rate, filling duration）, dry matter accumulation, leaf photosynthetic characteristics, and maturity yield with its components were measured across different treatments．Results showed that potassium application significantly improved maize grain filling rate and duration, promoting dry matter accumulation, with K₂ and K₃ treatments showing the most significant effects．Logistic equation fitting results indicated that maximum grain filling rate, average filling rate, and filling duration under K₂ treatment increased by 18.6%, 23.4%, and 5.7%, respectively, compared with K₀ treatment．Meanwhile, potassium application enhanced post-flowering leaf photosynthetic rate, delayed leaf senescence, and strengthened source-sink coordination．Potassium application also significantly increased ear number, grain number per ear, and thousand-grain weight, thereby improving yield．Grain yield in K₂ and K₃ treatments increased by 21.3% and 22.5%, respectively, compared with K₀ treatment．When potassium application was 360 kg/hm², all grain filling parameters and yield indicators showed no further improvement, but rather a slight downward trend．Correlation analysis showed that maximum grain filling rate, average filling rate, and filling duration were significantly positively correlated with yield（correlation coefficient was 0.892, 0.915 and 0.873）．Appropriate potassium application rate for summer maize in north China plain ranges from 180 to 270 kg/hm², which significantly improved maize grain filling characteristics, promoted dry matter accumulation, and achieved higher yield．Research results provided a theoretical basis for rational potassium application in high-yield cultivation of summer maize in north China plain．