The paper describes modal analysis of lifting platform usually used in theatre technologies. The platform itself consists of several components mutually connected by joints. The behavior of particular joints can be linear or nonlinear. The connection of two main parts - tables and pillars of lifting platform-must be considered as nonlinear because the force transfer between these parts can occur only in one direction. Since standard modal analysis is in principle linear, the method of linear description of nonlinear behavior has to be proposed. The contribution presents such method using application of three different boundary conditions which allow describing the nonlinear behavior of system by tools of linear analysis. Consequently, the modal analysis of the entire system is performed for all three types of boundary conditions. On the base of mode shapes visualization the proper mode shapes are extracted which satisfy the real behavior of the lifting platform.