Abstract: The contribution of different sources of nitrogen loading in the Erhai Lake eutrophication was studied by analyzing the morphology and characteristics of temporal and spatial variation of nitrogen loading. The sources included the rivers flowing into Erhai Lake, dry and wet deposition, and sediment release. In 2010, the TN loading of Erhai Lake decreased 28% than that in 2008, and the rivers flowing into Erhai Lake was the main TN loading source by contributing 37% with a significant positive correlation with its contents of TN and Chla. The main morphology of rivers TN loading was the NO₃^--N, which contributed 39% to the total entering nitrogen loading. The nitrogen loading of rivers into the lake significantly varied with seasonal changes reaching the peak value in July and showing largely spatial differences. The three rivers in the north region was the main source, and the Miju River provided the greatest contributions of 57% to the total river entering TN loading. The endogenous TN loading from the sediment releasing was about 29% of the TN loading and this showed a significant positive correlation with the content of Chla. Its morphology was mainly NH₄⁺-N and contributed 98% to the total fluxes of nitrogen. The highest value of the diffusion flux of TN and NO₃^--N in the sediment was in the northern region, and that of NH₄⁺-N was in the southern. The maximum value occurred in September and the minimum value occurred in December. The nitrogen loading by the dry and wet depositions changed significantly with seasons, and its morphology was mainly in the form of NH₄⁺-N. Its maximum value occurred in June. The critical period should be the beginning of the rainy season to control of external nitrogen loading into Erhai Lake, and Miju River and its watershed was the key area. Consequently, the agricultural planting structure in this area should be taken into account and the ecological restoration would be applied to control the endogenous sediment release.