In order to study the safety disposal of a typical retired soil-covered oil tank, a nitrogen inert experiment was carried out based on the design of a simulated soil-covered oil tank based on prototype size. According to the similarity theory, a nitrogen inserting simulation experimental system was designed to determine the experimental contents and steps, and the oxygen replacement efficiency and the space-time distribution of oxygen in the oil tank were studied. The results show that under the same nitrogen flow, the oxygen concentration and time show a logarithmic relationship, with the increase of time oxygen concentration decrease rate gradually, the oxygen concentration in the tank at the same time is basically the same. At the inlet, oxygen concentration fluctuates greatly at the initial stage of inerting and tends to be stable at the later stage. With the continuous increase of the flow rate in the same position of the tank, the shorter the time required to reach the set oxygen concentration, the higher the inerting efficiency. The research results have great significance for the safe disposal of oil and gas leakage from decommissioned soil-covered tanks.