Abstract: The oil and gas in the primary/secondary sealed space of floating-roof tank may cause fire accidents under the action of lightning striking. In order to study the distribution law of oil and gas in the primary/secondary sealed space of floating-roof tank and influencing factors, a floating-roof tank experimental model is established. Under different wind speed and temperatures, the oil and gas volume fractions at different positions in the primary/secondary sealed space are detected and analysis of oil and gas diffusion mechanism is carried out. Through reasonablely assuming unknown parameters and putting the intrinsic parameters of the experimental model into the numerical formula, oil and gas changes presented by these two methods are in good agreement, thus more detailed distribution law of oil and gas and influencing factors are worked out. Results show that with the leeward point as the starting point, the oil and gas volume fractions at different positions of the primary/secondary sealed space rise all the way and reach up to the peak near the upwind point. The increase of temperature and wind speed can both make the distribution differences of oil and gas in the primary/secondary sealed space increase, and the influence of wind speed on the uneven distribution is more obvious compared with that of temperature.