In order to coordinate development of population, economy, and environment, it is necessary to clarify the causal relationships among population agglomeration, economic agglomeration and environmental pollution. Based on the provincial data from 2007 to 2016, this paper uses the panel data unit root test, the panel cointegration test, and the panel error correction model (PECM) to generate the dynamic generalized least square (DGLS) estimation in order to explore the long-term and short-term causality among the three variables. The results show that for the short-term relationship, there is a one-way circular causal relationship among population agglomeration, economic agglomeration, and environmental pollution, while for the longterm relationship, these three variables demonstrate a double-circular causality. Based on the difference between the long-term and short-term causality, China should pay more attention to the development of regional economy, population urbanization, and environmental protection in order to realize the coordinated development of these three elements.