The effect of three yearss traw returned to soil and application of potassium fertilizer on winter wheat-summer corn yields and topsoil potassium was conducted in the low fertility of efluvo aquic soil in North China Plain.The result showed that yields of wheat and corn in treatments NPK and NPK+St were significantly increased in contrast to that in treatment NP;the highest yield increment was achieved in treatment NPK+St which also decreased yield coefficients of variation in different years.Straw returned to soil significantly increased some forms of soil available potassium content.Under the same crop growing,the recovery efficiency of applied potassium,agronomy efficiency of applied potassium and partial factor productivity from applied potassium in treatment NPK+St were higher than that in treatment NPK.Furthermore,these contents of soil available potassium,non exchangeable potassium,mineral potassium and total potassium in topsoil of 0~20 cm were increased in treatment NPK+St.Therefore,straw returned to soil could be beneficial to stabilize and improve different forms of soil potassium,and treatment NPK+St could not only get high and stable crop yields,but also increase different forms of soil potassium content.