With the increasing demand for oil storage, storage tanks are developing towards large-scale tanks better adaptability to extreme working conditions. The variation law of the oil temperature field and the flow field inside the tank should be accurately understood to guarantee safe and economical operation of an oil depot. Aimed at understanding the periodic variation in the ambient environment of the tank's location and the physical properties of the crude oil, the theoretical model of unsteady heat transfer flow in a large floating roof tank was established by using the relative heat transfer theory in this paper. The numerical solution technique for the crude oil temperature field and the flow field was studied. This paper thoroughly analyzed the effect of heat transfer and flow coupling characteristics on the tank static storage process under the influences of the atmospheric temperature, solar radiation, etc. The results show that according to the variation law of the temperature field, the static storage cooling process was divided into a partial rapid cooling stage, overall rapid cooling stage, condensate reservoir growth stage and overall low-speed cooling stage. The heating process was divided into a partial low-speed heating stage and partial rapid heating stage. The solar radiation has a great influence on the temperature fluctuation, and the atmospheric temperature has a great influence on the rate of temperature decrease. The results can provide theoretical support for optimizing the design of the storage process and managing the manufacturing of a large floating roof tank. (C) 2018 Elsevier Ltd. All rights reserved.