The object of research is a statically determined symmetric planar model. Assume that the truss bars have the same stiffness and cross-section and that the truss masses are evenly distributed at their nodes. Method. The Dunkerley formula and a simplified method are proposed to estimate the lowest limit of the natural vibration frequency of a truss with an arbitrary number of plates. Solving the system of linear equations determines the force in the rods, and all analytical transformations are performed in the Maple computer mathematics package. Using the Maxwell-Mohr formula, find the stiffness matrix of the structure. Results. The first natural frequency of the truss obtained by the analytical method is compared with the results of the numerical method. The frequency spectrum of the truss was analyzed, and conclusions were drawn about the frequency dependence on the size of the truss rods.