Abstract: The aim was to provide important theoretical basis of potash fertilizer application in soybean production. From V₃ stage, four consecutive potassium deficiency treatments were set to determine effect of potassium deficiency stress on the accumulation of potassium and dry matter in soybean plant with sand culture. The result showed that under the condition of potassium deficiency, potassium transferred from lower to upper leaf and petiole for the growth of new organs in V₃ to R₁ stage. Potassium transferred from vegetative organ to pod to ensure pod’s growth and development from stages of R₁ to R₃, R₃ to R₅ and R₅ to R₆. The potassium deficiency had little effect on dry matter accumulation in stages of V₃ to R₁ and R₁ to R₃ which were mainly vegetative growth. The accumulation of dry matter declined obviously when potassium deficiency was in stages of R₃ to R₅ and R₅ to R₆, which were pivotal to the effect of potassium on dry matter accumulation.