Abstract: How to set the carbon tax rate? What factors enter into the decision? Are there differences among regions of big economy? This paper adds energy and carbon tax into aggregate production function, builds a dynamic optimization model in the environment constraints, solve the optimal carbon tax rate, and calculate it based on panel data of China. We find that, a series of positive influence factors and a series of negative influence factors, meanwhile the differences of optimal carbon tax among regions are significant. It means that the process of setting carbon tax rate must be under the principles of equity and common but differentiated responsibilities and respective capabilities.