Storage tanks are among the most important components of heat storage systems. Long preheating time causes low operating efficiency and high economic costs. In this work, the temperature distribution, thermal stress distribution, and related influencing factors of storage tanks are studied by the computational fluid dynamics (CFD) method. In addition, a new preheating scheme is proposed to optimize the preheating process of a storage tank. The results show that as preheating proceeds, the temperature distribution of most parts of the tank becomes increasingly uniform, and the thermal stress greatly increases. Local thermal stress can be concentrated at the joint of the tank sidewall and tank bottom. Increasing Ta and Gg can shorten the preheating time of the tank but also increase the risk of thermal stress concentration in the tank. With traditional preheating methods, decreasing the TD can improve tank preheating characteristics but may possibly cause local thermal stress concentration in the tank. The equal difference-variable stepped preheating method is proposed to optimize preheating characteristics. The optimal preheating scheme to efficiently and safely preheat the tank is when T = 15 K, which is reduced by 55.1% in comparison with the preheating scheme of the actual project. (C) 2020 Elsevier Ltd. All rights reserved.