With the increase in demand for oil storage

the scale of tanks are developing towards the direction of large scale and better adaptability to extreme working conditions. The change of oil temperature field inside the tank should be accurately grasped

which is of great significance to guarantee safe and economical operation of oil depot. Aiming at the periodic change conditions of tank ambient conditions such as solar radiation

atmospheric temperature and etc.

a theoretical model of the unsteady-state heat transfer process of large double-deck floating roof tank is established by using the theory of heat transfer

and the forward difference equations of boundary point are obtained by model region discretion. On basis of determining the physical properties of crude oil in the storage tank

heat transfer coefficient of the tank as well as the heat flux density of boundary

the numerical stimulation method of temperature field in the tank can be studied. The analysis and application of a 10×104 m3 floating roof storage tank in Daqing has shown that the temperature drop rate increases with the decrease of the solar radiation intensity and the atmospheric temperature. The effect of solar radiation on temperature drop rate of tank shell is small

which increases with the decrease of atmospheric temperature. The tank bottom is approximate to adiabatic state and the effect of the external environment on temperature drop rate is small. The results can provide theoretical support to optimize the storage process design and manufacturing management of large floating roof tanks.