In agriculture production, it is very common to apply considerable quantities of nitrogen, phosphorus and potassium fertilizers by compounding or apply compound fertilizers, thus nutrients translocation, transformation, uptake and metabolism will be influenced profoundly by interaction of nitrogen, phosphorus and potassium in soils. In this article, the effects of monocalcium phosphate and potassium chloride on water-soluble ammonium nitrogen and nitrate nitrogen in paddy soil treated with ammonium chloride were studied. The results showed that content of water-soluble ammonium nitrogen decreased and that of nitrate nitrogen increased with the extension of culture time, and there was significant correlation between the decrease of water-soluble ammonium nitrogen content and the increase of nitrate nitrogen content. The content of water-soluble ammonium nitrogen in soil treated with monocalcium phosphate and ammonium chloride was significantly higher than that of soil treated with ammonium chloride at the middle culture time, because the transformation of ammonium nitrogen to other forms of nitrogen was retarded by monocalcium phosphate, the conten of nitrate nitrogen was inhibited by monocalcium phosphate at the middle and late culture time. The content of water-soluble ammonium nitrogen in soil treated with potassium chloride and ammonium chloride at the early and middle culture time increased compared with that of soil treated ammonium chloride, and the content of nitrate nitrogen was inhibited by potassium chloride at the late culture time. Thus, application of ammonium chloride and potassium chloride, or ammonium chloride and monocalcium phosphate, or ammonium chloride and monocalcium phosphate and potassium chloride together play important roles in improving nitrogen use efficiency and reducing nitrate leaching loss.