Abstract: With the aim to provide the theoretical basis for sustainably increasing crop yield, productivity, and nutrient management in fluvoaquic soil of Hebei Province, the effects of the longterm application of K fertilizers and straw returning on crop yield, soil K content and potassium balance were analyzed using the data obtained from the longterm K localization experiment (1992-2009) under wheatmaize rotation system. The results reveal that the 17-year average yields of wheat and maize are in an order as NPKSt NPK NPSt NP, which is similar to the effects of the K fertilizer application. Compared to the NP mode, the yields of wheat and maize under the NPKSt mode are increased by 9.37% and 19.23% respectively, the yields of wheat and maize under the NPK mode are increased by 6.32% and 18.25% respectively, and the yields of wheat and maize under the NPSt mode are increased by 2.76% and 9.60% respectively. The nutrient analysis indicates that the contents of available potassium and slowly releasing potassium in the 0-20 cm soil layers under the modes of NPKSt, NPK and NPSt are significantly different from those under the NP mode, showing an order as NPKSt NPK NPSt NP, while no significant differences in the contents of available potassium and slowly releasing potassium in 20 to 40 cm soil layers are found between the four fertilizing modes. The nutrient balance analysis discloses that the profit and loss annually of K under the NP mode is -170.0 kg/ha, indicating that potassium is seriously deficiency in soil, the real surplus and deficit rate under the NPSt mode is -584% and the annual profit and loss of K is -150.6 kg/ha, the profit and annual loss of K and the real surplus and deficit rate under the NPK mode are nearly in balance and they are -3.1 kg/ha and -1.0% respectively, while under the NPKSt mode, the balance index of K is 1.37, the real surplus and deficit rate is 36.8% and the profit and loss annually of K is 111.4 kg/ha. These results demonstrate that the longterm application of K fertilizers and straw returning in fluvo-aquic soils of wheatmaize rotation fields have significant effects on yield increase and soil potassium balance.