Abstract: This paper deals with the modal analysis of a multi-span beam with intermediate flexible constraints and different boundary conditions. Each span of the continuous beam has a different span, a different stiffness and the mass per unit length, which is assumed to obey Euler beam theory. Considering the compatibility requirement on each constraint point, characteristic equations for a simply supported beam, a cantilever beam, a fixed-fixed beam, a free-free beam are presented. Based on the theoretical and numerical analysis, the comparison between the current method (transfer matrix method) and a conventional method (equation of three moments method) is conducted for the validity. Finally, some numerical results are shown to present the influence of intermediate support stiffness and boundary conditions on the mode of multi-span beams.