Based on the combination of Rayleigh and Southwell’ s methods

fundamental frequency of structures could be denoted as a composition of frequencies of several subsystems

which consists of deformation components and inertia components.Deformation components include flexural deformation and shear deformation

and inertia components include structure distributed mass and added mass on tower top.Through choosing deflection function satisfying boundary condition

the relationship between funda- mental frequency and stiffness of tower structure with fixed bottom and top concentrated mass could be found.Thus tower structure’ s bending and shear stiffness could be recognized through measuring its vibration fundamental frequency.The algorithm was applied to a steel tower and to deduce the relationship of tower’s fundamental frequency and its elastic modulus.Each section’s stiffness could be quickly identified as long as its geometric size and material properties were known.Finite element method（FEM） was utilized to prove high precision of this algorithm.The method is suitable to tower structures with fixed bottom

and can provide valuable information for monitoring and evaluating the operation state of tower structure.