Abstract: Potassium fixation by soils was studied for 25 soil samples taken from major agricultural regions of north China with 0~4000 mg K added to each kilogram of soil. Potassium fixation can be well discribed by an equation y=ax3/2/(x3/2+b) (y is the amount of K fixed in mg/kg, x is the amount of K added in mg/kg, a is an estimation of maximum potassium fixation in mg/kg, b is a constant ). Fixation power of the various soils differred significantly, the amount of K fixed was closely related to the types and the amount of clay minerals existing in the soil, and physical and chemical properties (clay content, CEC, non-exchangeable K and available K levels). Potassium fixation by soils was negatively correlated with non-exchangeable K content of the soils. Soils taken from different regions showed different K fixation characteristics. When K application level was below 1200mg/kg soil, capacity of K fixation of these tested soils followed a general order: soils from northwestern region soils from northeastern region soils from northcentral region;while K added was above 1200mg/kg, K fixation power of the soils showed a general tendency: soils taken from northwestern region soils from northcentral region northeastern region. When 400~4000 mg K was added to one kilogram of soil, on average, 133 ~ 348 mg / kg were fixed by soils from northwestern region with an average maximum fixation of 372 mg/kg; 235~1001mg/kg were fixed by soils from northcentral region with an average maximum fixation of 1121 mg/kg; 199-1254 mg/kg were fixed by soils from northeastern region with an average maximum fixation of 1519 mg/kg soil.