Abstract: Based on the mass conservation principle, applying one-dimension convection-diffusion equation, hydrocarbon concentration field models in height of vapor space is described and several boundary terms are presented according to actual operation conditions. An arbitrary Lagrange-Euler method is introduced for coordinate transformation aiming at the characteristic of varying calculation domain and moving boundary between liquid phase and vapor phase during liquid cargo storage and transportation. Forward time, centered space finite difference method with fixed step for space and varying step for time is applied to the dispersing model. The rationality of models and validity of the dispersing method are verified by several numerical examples. The result from the numerical simulation provides a theoretical consideration for the optimizing policy of cargo operations.