Abstract: Existing methods don't take the compressibility and molecule interaction of multi-component nonideal gas under high pressure into consideration fully, so they cannot reflect diffusion characteristics of each component accurately. To solve this problem, the Fuller binary diffusion coefficient and thermodynamic factor calculation methods were modified based on the PR equation of state. Then, the effects of gas pressure and component on thermodynamic factor were analyzed. Finally, Fick diffusion coefficient matrix of three-component system was calculated. It is indicated that as for real multicomponent nonideal gas, the accuracy of the modified diffusion coefficient calculation method is increased significantly.The thermodynamic factor characterizes the deviation degree of real state from the ideal state of mixture and the relationship between molecule diffusion direction and concentration gradient. And it varies with the system pressure and the gas component and its variation trend is the same as that of compressibility factor. The studies on the modification of multicomponent nonideal gas diffusion coefficient lay the theoretical foundation for exploring the diffusion of multi-component nonideal gas in air.