Abstract: Identifying oil and gas evaporative emission mechanism and controlling oil and gas emissions are the most fundamental means to maintain product quality, prevent oil and gas explosion, reduce air pollution, and realize the storage and transportation safety and energy conservation and emissions reduction. There are many factors that influence oil evaporative emission in such confined spaces with specific openings like oil tank. In this paper, the mechanism of mass transfer between gas and liquid is analyzed under the condition of sloshing, revealing the impacts of liquid compartment sloshing caused by external disturbances like ship swaying, cargo loading and unloading on gas-liquid mass transfer rate of oil and gas and the corresponding changes of physical fields. Concept and design of the modeling are described in detail, and the analysis of some typical experimental results and related experimental phenomenon is given. This research is conducive to the safe operation of offshore oil and gas storage and transportation, which can provide a theoretical basis and data support to the optimal control of liquid cargo handling, and breathing valve opening/closing.