The dynamic characteristics of a TV tower with 610m in height is actively analyzed by using commercial package ANSYS in this study. The mode selection is carried out by determining the modal mass participation ratio. The observations made based on numerical investigation demonstrate that the natural frequencies of the high rise unsymmetrical tower are substantially close and the modal displacement of the antenna is much larger than that of the major tower. In order to select the major mode shapes, the modal mass participation ratios of the first 30 modes are calculated and at least first 10 mode shapes should be considered when investigating the seismic responses. It is seen that the mode shapes whose vibration directions are paralleled to the short axis of the elliptical core tube are critical to the structural seismic responses. In this direction, the mass participation ratios of the first three mode shapes add up to 0.63, the 10 modes, the sum of whose modal participation ratio is 0.8184, are selected in order. Therefore, at least 10 modes should be involved in the analysis of structural seismic responses.