In the process of urban agglomeration development, the intercity competition and cooperation are parallel, and the relationship between the cities has important impact on urban development and the overall economic development of urban agglomerations. Based on spatial spillover effect to construct spatial econometrics model, we choose the data of 26 cities in the Yangtze River Delta urban cluster as sample, analyze the influence of the intercity competition and cooperative on the cities and the economic development of other cities. Empirical results show that competition has a positive effect on the level of local economic development but its impact on other cities is negative, and that the effect of cooperation on the level of local economic development is positive and its impact on other cities is also positive. Under the examination mechanism taking economic performance as the core of local government, the negative spillover effect of competition and positive spillover effect of cooperation make the willingness of the competition be greater than that of cooperation among local governments. Therefore, these areas should bring governmental role into fully play, take “intercity cooperation” as the important content of the examination of each city government and officials while making good overall plan for urban agglomerations, meanwhile, set up effective and normalized intercity economic cooperation mechanism and strengthen intercity economic cooperation relation and behavior by industrial division.