The heat loss and surface temperature of the top surface and sidewall of large-scale floating roof tank is tested by the heat flow meter and surface temperature method. Based on the test data, the heat loss from the top surface is about twice more than that of the sidewall which means the top surface is the weakest insulation part of the floating roof tank. On the surface, the heat loss profile is in accord with the surface temperature distribution. Special attention is given on the calculation of thermal conductivity for the top surface and sidewall which finally deduced the total heat transfer coeffi- cient of large floating roof tank. Moreover, the heat loss of floating roof tank in different working conditions is predicted. According to the calculation results, the level of 6m is regarded as a critical level determining the heat loss. And the cen- tralization storage of oil is a more energy conservation storage pattern. Nowadays, in order to avoid the energy crisis, an increas- ing attention is given on the energy storage in many coun- tries. As one of the most important primary energy, the stor- age of crude oil always dominates in the existing energy sys- tem. With the increasing storage scale of crude oil, the heat dissipation during the storage course draws many people's attention. Especially in the cold region, for the storage of waxy crude oil, the heat loss is considerable. For many large crude oil depot, the floating roof tank has become the pre- ferred facility to store oil. But due to the specific construc- tion, the heat loss from the different part of the tank is diffi- cult to ascertain. Normally, the theoretical calculation based on the heat transfer theory is induced to investigate the heat loss, Busson and miniscloux (1) developed a simple model to predict the steady state heat losses from a fuel oil tank based on the as- sumption of a well-mixed core of fluid. Kumana and Kothari (2) proposed empirical correlations for heat transfer coeffi- cients of the tank and published a model to predict the cool- ing rate of oil. Venart (3) solved the governing natural con- vection equations to investigate the steady state heat losses from a fuel oil tank. Cotter and Michael (4-6) presented a simplified heat loss model based on the numerical calcula- tion of heat transfer in the oil tank. Moreover, the effect of heat transfer coefficient, aspect ratio and temperature de- pendent viscosity on the fluid flow and heat transfer was examined. In general, most research takes the dome roof tank as the research object, the heat loss rule of which is very different from the float roof tank due to the different roof construction. Together with the complex heat transfer course which is difficult to characterized, the actual measurement is still regarded as the most effective method. As mentioned above, the actual measurement of heat loss from floating roof tank has not been reported in the litera- ture. The aim of this work is to investigate the heat loss from the different part of the floating roof tank, and special atten- tion is given on the heat flux from the top surface and the calculation of thermal conductivity for air layer in the top surface. The surface temperature of the tank is also tested to estimate the inner temperature profile of oil. Moreover, the total heat transfer coefficient of large floating roof tank is proposed to predict the heat loss in different working condi- tion which is significant for the management of the oil depot, in the meantime provides the basis for the energy-saving and efficient storage of crude oil.