In the newest design based on performance, a reliable seismic demand assessment is considered to be one of the fundamental cornerstones. Considering the uncertainties that exist in this estimation, different methods have been proposed for doing so. Is. Today, among these multiple methods for seismic demand estimation, the estimation method based on the parameter of intensity index is more acceptable. There are two key points in this method: first, the intensity index parameter and the second accelerated values ​​used in dynamic analysis, which assesses the role of each of them on the results from the main goal of this study. In this research, three models of steel, 3, 9, and 15 steel frames were modeled in OpenSees software and a nonlinear incremental dynamic analysis was performed on them. The seismic demand was estimated using two parameters of maximum acceleration and acceleration intensity The spectrum of the first mode was determined and the results were analyzed according to the different parameters of the accelerometer and the intensity index parameter. The results of this study in general indicate that the spectral acceleration of the first mode due to the lower standard deviation in the data dispersion is the more reliable index of intensity compared to the maximum acceleration of the earth and indicates that their selection is based on logical seismic parameters Their selection is based on domain values, which is a remarkable result.