Abstract: The modal properties of two practical cable-net structures, as examples, were analyzed with the sub-space iteration method to investigate the characteristic of frequency distribution of general cable-net structures and the effects of structural parameters, such as steel cable stiffness, structure mass and rise to span ratio, on their free vibration properties. In addition, the modal analysis considering geometry update was carried out. The research results show that the vibration modes of a cable-net structure are close each other, the initial tensile force and the structure mass are two important factors influencing the free vibration properties of a cable-net structure.