Abstract: LNG roll-over will bring tremendous threat to the safe operation of the storage tank. Physical and mathematical models of LNG roll-over in storage tank are established. For the 16×10⁴ m³ storage tank commonly used in LNG terminal, its LNG roll-over process is numerically simulated under initial density differences using Fluent software, and the variation of LNG roll-over in storage tank with initial density difference is obtained. The results show that, the larger the initial density difference, the sooner and more intense roll-over happens; the LNG density difference is existence, when the initial density difference is less than critical density difference, the mixing process of two adjacent LNG layers in storage tank is relatively stable; when initial density difference is more than critical density difference, the roll-over strength increases significantly. Roll-over coefficient is proposed and defined as a criterion to judge the LNG roll-over strength. Through calculating, the critical density difference of 16×10⁴ m³ storage tank is from 2 to 4 kg/m³.