As an important theory of social complex ecosystem, urban niche has always been the focus of research, but there is a lack of in-depth observation of scale effect at present. Taking Zhejiang Province as an example, this paper made a horizontal comparison of three scales of city-district-town for the first time, and constructed an urban niche evaluation model applicable to multiple scales. In this study, niche width, niche overlap, niche differentiation index and gravity model were used to investigate the niche of 825 townships, 71 districts, and 11cites at three scales. The results indicate that: from the perspective of niche breadth, the niche development of Zhejiang Province is unbalanced, and the city scale presents an anti "C" structure. Quzhou city and Lishui city have the smallest niche breadth, while Hangzhou city, Huzhou city and Ningbo city have the largest niche breadth. The larger the research scale and niche width, the greater the scale effect. From the perspective of niche differentiation, the degree of niche differentiation gradually increases with the decrease of scale, and the degree of social niche differentiation is the largest. It shows that the more unbalanced the development is, the greater the scale effect is. Furthermore, from the niche overlap degree and gravity model, the study found that the regions with small niche width often faced greater competition and were difficult to get out of troubles, while the regions with large niche width were more likely to transform competition into cooperation. As a result, there is a polarization phenomenon that the stronger the stronger and the weaker the weaker. The competition between Lishui city and Quzhou city is the fiercest, while the cooperation between Hangzhou city and Ningbo city is more convenient. Therefore, cities in Zhejiang Province can optimize regional development through resource reengineering, synergistic development and supporting strategies.