Based on the principle of the space action of framed tube (or tube in tube) structures, a simplified calculating method is presented. The method uses equivalent columns in replacing the framed tube. Curves and tables used for computation are given. The effect of changing the number of stories on the space action of structures is analyzed. This simple and practical method can be used for calculating structures as well as for determining structural parameters in selecting a scheme and preliminary design. The computation can be performed with or without the aid of computer. According to the principal characteristics of framed tube structures, some problems concerning scheme design are discussed.