Abstract: Study was carried out on fluvo-aquic soil of low fertility coming from Huanghe River plain for 18 years. The research of potassium forms applied a chemical analytic method. The results show that the straw returning combination to fertility improves release of slow-release K and available K, and availability of mineral K. As straw application rate at the range of 2250、4500、6750kg hm-2,soil non-exchangeable K, water soluble K, specifically absorbed K and non-specifically absorbed K are all positively related to the amount of straw remarkably, while mineral K is negatively correlative. The variant regularity of soil K is that non-exchangeable K and specifically absorbed K are increasing, but the other forms of K are decreasing.