There are many problem of urban sewage treatment facilities in China, such as small scale and unbalanced distribution, which means optimal allocation of urban sewage treatment facilities is significant. Based on the principle of efficiency maximization and cost minimization, this paper aims to establish a new method for optimal allocation. Taking Xucheng Town in Huaian City Jiangsu province as a case, this paper established models of "target market share" and "the minimum impedance" by the ArcGIS network analyst tool. The result shows: One of the current sewage treatment facilities is operating reasonable, while the other one is inefficient because the equipped network is not enough. Then, the former facility can maintain, while the latter facility should expand its equipped network. The total treatment capacity of the current two facilities is still shorter than the whole emission of waste water in town. So a new sewage treatment facility should be built in the recent future. According to the related plan, the designed capacity of the new facility should be 20000t/d. The best location of the new facility is the minimum cost location. The problem of sewage treatment facilities in Xucheng Town is common in China, so the method is referential, which can achieve the collaborative optimization of micro-efficiency and macro-arrangement.