The paper considers the causal relationship about CO2 emissions, traffic density and urbanization development in China's provinces by the quantile causality test The method can capture the structural breaks under different quantiles from the nonlinear perspective. The robust results don't find the causality relationship between traffic density and CO2 emissions. Urbanization will increase CO2 emission at the high quantile level while the impact of CO2 emissions on urbanization presents a symmetric relationship. The promoting effect of transportation on urbanization only occurs at the beginning of urbanization. It shows the environmental pollution is a key factor to the whole process of urbanization. With the advancement of urbanization, the increase of traffic line density has no significant impact on the urbanization process. The results can provide references for the government in the layout of local traffic lines and the improvement of urbanization.