Sediments play an important role in nitrogen (N) and phosphorus (P) cycling and eutrophication in lakes. Spatial and temporal variations of ammonium nitrogen (NH₄⁺-N) in sediments were monitored for one year (May 2003-May 2004) at 5 sampling sites (Haigeng, Dounan, Luojiacun, Xinjie and Kunyang) typical of Lake Dianchi with the aid of the GPS technology, for analysis of characteristics of dynamic variations of NH₄⁺-N in sediments of different depth, different times and different regions of the lake. Results show that the NH₄⁺-N contents in the sediments averaged 74.57mg kg^-1 and varied in the range of 45.55~170.1 mg kg^-1within a year. It varied sharply with seasons, showing a general trend of being high in summer and low in winter, but the trend differed slightly from site to site NH₄⁺-N contents in sediments also varied significantly with depths, showing a trend of surface (0~5cm) > middle (5~10cm) > bottom (10~20cm) in summer and of middle > surface >bottom in winter. In three layers of sediments it varied in the range of 18.71~172.9 mg kg^-1, 29.55~192.2 mg kg^-1 and 19.93~123.8 mg kg^-1, separately. In terms of mean NH₄⁺-N content, Luojiacun was the highest and Dounan was the lowest. NH₄⁺-N in the sediments showed an extremely significant positive correlation with NH₄⁺-N in and pH of the waterbody, but a significant negative correlation with available-P in the sediments, which indicates sediment NH₄⁺-N is the source and sink of NH₄⁺-N in the waterbody and influence release of phosphorus from the sediments.