In the filling and transportation processes of liquefied natural gas (LNG), the safety of LNG storage tanks is compromised because of rollover phenomenon. As such, the rollover factors of LNG in a storage tank should be identified to prevent or weaken the rollover intensity of LNG. In this study, the rollover behavior of LNG in a storage tank is numerically simulated. The density of the two layers in a LNG storage tank is related to temperature in our numerical model. It is found that the greater the significant initial density difference (range of 1-12 kg·m^-3) is, the more obvious the LNG rollover will be. A density difference of 7.5 kg·m^-3 is found as the critical density difference in the present work. When the initial density difference exceeds the critical density difference, the LNG rollover coefficients increase dramatically. Moreover, an LNG rollover model with two daughter models is proposed, which are divided by the critical initial density difference, i.e., a cubic relationship between rollover coefficients and the initial density difference when the density difference is less than 7.5 kg·m^-3 and secondly, a linear relationship between the rollover coefficient and the double exponential functions when the density difference is larger than 7.5 kg·m^-3.