Abstract: Most solis in North China Plain were developed on the alluvial deposite of Yellow River with high mineral potassium contents.So it is not necessary to apply potassic fertilizer to the low and medium production farmland.Otherwise,"Luxury Consumption"would ocurr. Then potassium balance studies in agroecosystem are especially necessary for crop production.Based on a three-year experiment K balace and K supplying capacity of the soils in North China Plain were analysed in this papers.