This paper studies the optimization and coordination of the low-carbon supply chain considering triple bottom line under carbon tax policy. First, we study the decisions of the centralized supply chain considering the triple bottom line. Secondly, we consider four different decentralized supply chain models under the wholesale price contract, i.e., Model I, Model II, Model III, and Model IV. Then we study four different decentralized low-carbon supply chain models under two-part tariff contracts, i.e., Model I-LTT, Model II-LTT, Model III-LTT, and Model IV-LTT. The results show that the two-part tariff contracts can coordinate the low-carbon supply chain perfectly in Model I-LTT and Model III-LTT. At the same time, the low-carbon supply chain in Model II-LTT and Model IV-LTT can realize Pareto improvement. Finally, we conduct the numerical analysis to study the impacts of carbon tax and carbon emission reduction (CER) investment coefficient on the supply chain profits before and after coordination. This paper provides the reliable theoretical basis for low-carbon enterprises to choose CER strategies and contracts.