Wetland functions are closely related to the spatial scales. Research on the effect of spatial scales on wetland functions is therefore of great importance for guiding the spatial protection and management of wetland ecological system. The paper takes Yancheng wetland as a case study to explore wetland function evaluation methodology based on ecological niche theory.The related study of Niche Theory were focused on species or communities surviving conditions in a certain habitat,as well as their playing roles. The development and conservation for wetlands also can be considered by integrating the ecological and economic factors together. Based on the ecological niche theory, the Ecological-Economic Units (EEU) in wetlands was defined according to their ecological and economic functions. The function position for each EEU is determined by its available resources condition and the requirement of its products for social and economy. Among which, the "ecostate" in EEU was referred to the potential functions, and the "ecorole" referred to the ability of function changes. In addition, the Ecological-Economic Niche (EEN) is also defined as the situation of EEU be in possession of available resources or the function position of EEU. Namely, the EEN is the position and function of EEU in the wetland system. We also defined the most adaptive niche in the paper which refered to the highest ecological value or can provide highest net-economic benefits. Involving the most adaptive niche and the reality niche of wetland functions, the ecostate and ecorole of the EEN for wetland functions is formulated. The ecostate of ecological functions, for example, is the nearness degree between the most adaptive ecological niche and reality ecological niche. While the ecorole represents the trend of reality ecological niche to the most adaptive ecological niche. The EEN of wetland functions is formulated by the ecostate and the ecorole. The value of EEN is greater, the more efforts for protecting the EEU are necessary; otherwise the development will go ahead.Based on the above information, an ecological-economic niche model was developed to evaluate the wetland functions in Yancheng coastal wetland. We explored the wetland functions at four different spatial scales including 1km 1km, 2km 2km, 4km 4km and 8km 8km. The results indicated that: (1) With the increase of the spatial scale for evaluation, the wetland area with the highest ecological and economic functions is decreasing, and the reductions are gradually increasing; the wetland area with the lower functions is increasing, and the increased areas is multiplied with the scale enlarged. (2) With the increase of the spatial scale for evaluation, the spatial forms of wetland at different function levels were changed accordingly. Especially, the spatial forms of wetland at relatively lower or higher functions levels showed a significant change. (3) Reasons for the above mentioned results are that the variation of estimated units in spatial scale would make the structure of land use types also changed, which lead the dominant wetland functions to be changed. (4) The results of large spatial scale evaluation are more in line with the characteristics of "Rolling Development" model of the Yancheng Coastal Wetlands, and therefore of great significance in guiding the wetland functions zoning, wetland use planning and wetland management.