The present research numerically simulates oil temperature field during long storage in large floating roof tank based on a physical-mathematical model established through analyzing the heat transfer process between tank oil and the environment. A serious of factors are taken into consideration, such as the turbulence inside the tank, the atmosphere, thickness of insulating layer, solar radiation, soil under the bottom, physical property of oil as well as the natural convection inside the tank. By comparing numerical simulation results with on-site monitoring data, the developed model is validated. Two tanks are selected for numerical simulation, according to which the oil temperature variations as well as the heat transfer characteristics at different conditions are studied. Also, the impact of floating roof type, insulation layer thickness and solar radiation is discussed. This study may provide valuable guidance not only for the future design of large floating roof tanks, but also for safe and energy-saving operation of large floating roof oil tanks. (C) 2018 Elsevier Ltd. All rights reserved.