Abstract: Because of dissolving ability difference among different gas components, dissolution itself could cause original components of natural gas to be changed. This is so called dissolution fractionation of gas components. Dissolution fractionation could happen during natural gas migration and dissipation in water. It is necessary to find out dissolution fracionation mechanism and establish fracionation model for tracing origin and distribution of natural gas. Based on the Henry's Law, a dissolution fractionation model of gas components was established. The model calculation shows that, the original gas components in the Sinian reservoir of Weiyuan field are CH4-72.70%, C2H6-0.09%, CO2-22.41% and N2-4.07%, and the dryness coefficient (C1/C1-5) is 99.876%. Because of dissolution the CO2 contents in natural gas decreased greatly while hydrocarbon gases contents increased slightly. Resumption of the original components of natural gas is helpful to genetic discrimination and gas-source correlation.