Abstract: This study aimed to identify the effect of different potassium supply levels on transportation and distribution of potassium and on grain yield in oil flax. Using the oil flax cultivar “Baxuan No. 3”, a field experiment was conducted with four potassium fertilizer application rates: control (K₀: 0 kg K₂O/ha), low potassium (K₁: 18.75 kg K₂O/ha), medium potassium (K₂: 37.5 kg K₂O/ha) and high potassium (K₃: 56.25 kg K₂O/ha) from 2011 to 2012 at Zhangjiakou, in Hebei Province, China. Significant differences in potassium accumulation of different organs, including root, stem, leaf and grain, were observed. However, the changes in K content of each organ during the whole growing period were basically consistent and closely related to the rate of potassium fertilizer. The potassium accumulation in root, stem, leaf and grain was greatest during the reproductive stage of growth, and accounted for 41.28%-64.09% of the accumulated potassium over all growth stages. Potassium uptake took place in all three organs: the root, stem and leaf. Compared with control (K₀), the potassium uptakes in root, stem and leaf under low potassium K₁ (18.75 kg K₂O/ha), medium potassium K₂ (37.50 kg K₂O/ha) and high potassium K₃ (56.25 kg K₂O/ha) treatments were increased by 35.60%, 29.06% and 43.75%, respectively. The potassium transportation rates from root, stem and leaf to grain were 17.78%-24.85%, 14.82%-23.00% and 39.40%-46.20%, respectively, and the contribution of transported potassium to the total amount of grain potassium in oil flax was 6.71%-14.12%, 11.24%-23.97% and 17.26%-50.83%, respectively. Meanwhile, compared with the control (K₀) treatment, grain yield increased by 14.90%-24.12%, 29.93%-30.11% and 15.65%-23.13%, respectively, under the 3 potassium treatments, K₁, K₂ and K₃. Considering potassium accumulation, transportation, distribution and crop grain yield, the optimal potassium fertilizer fertilization for oil flax was 37.5 kg K₂O/ha (K₂) under the climatic conditions of the experimental area.