In modern tall buildings, lateral loads induced by earthquake are often resisted by a system of belt truss, shear core or other structural systems. The best location of belt truss system, which results in the minimum roof displacement, plays an important role in structural design of tall buildings. Because of different optimum position of belt truss system due to variety in earthquakes, to achieve minimum roof displacement of the structure, it is essential to find a unique position for a given structure. This paper proposes a tool to determine the unique optimum location of belt truss system based on critical excitation method. Numerical examples are presented to demonstrate the efficiency of the critical excitation method in determining the unique optimum location of belt truss system. Results show that the absolute roof displacements which are induced by computed critical accelerations are between the range of 5.36 to 1.95 times of the Sen Fernando earthquake for the first example and 7.67 to 1.22 times of the Sen Fernando earthquake for the second example. Also, this method can be used to determine the minimum distance required between two adjacent tall buildings to eliminate the pounding effects.