Huashuang No.4 was selected to study the effects of potassium fertilizer on the whole stage of rapeseed growth including indexes of seedling stage,yield and yield components and finally to test the potassium uptake and use efficiency in the lab in Wuxue City,Hubei Province during 2008-2009.The optimum fertilizer application was calculated by establishing the model of economic region potassium.The results showed that the suitable application rate of potassium was helpful for the over-wintering stage of rapeseed seedling and significantly improved effective branches and pod numbers per plant.The results demonstrated that when the application of potassium was 180 kg/hm2,the total dry matter,seed yield and accumulation of potassium reached the largest which were 10 410,2 791 and 235.7 kg/hm2, respectively,and the net profit of K was 1 967 Yuan/hm2.Combining the model of fertilizer efficiency with the field trial,the optimum potassium fertilization rate of 160 kg/hm2 was recommended under the experimental field condition.