Taking the wing mounted, auxiliary-fuel-tank for large and medium-sized civil aircraft with subsonic speed and large aspect ratio as the research object, this paper analyzes relevant airworthiness terms of load-calculation in CCAR-25, considers the influence of the movement of external object itself and the elastic deformation of the wing structure on the aerodynamic load of auxiliary-fuel-tank, and gives the overload-velocity envelope, altitude-velocity envelope and load calculation for auxiliary-fuel-tank static-load calculation. On the basis of Transport Aircraft Load-calculation Programe-package, which is widely used in engineering, the wing was simplified as a cantilever beam for aeroelastic correction by the method of subsonic steady-state flow lifting line theory and wind tunnel test. The function module such as aeroelastic correction calculation of auxiliary-fuel-tank, inertial force calculation, real-time update of auxiliary-fuel-tank mass and envelope screening were studied. According to the engineering application, the calculation accuracy meets the requirements, forming the auxiliary-fuel-tank static-load calculation method which meets terms of airworthiness, standardizing the calculation process of the auxiliary tank static load and expanding the functions of Transport Aircraft Load-calculation Programe-package.