To accurately evaluate the safety and comfortability of structures after a long period of service under dynamic loads such as earthquakes and wind, it is critical to establish a structural dynamic model that can accurately reflect the dynamic responses of actual buildings under seismic, wind and other dynamic loads utilizing the monitoring/inspection data. In this paper, for popular frame building structures, an equivalent simplified dynamic modeling method is proposed by using a few numbers of wireless mobile sensors. First, the principle of equivalent interstory shear force for a simplified model of buildings is proposed, which proves that the simplified model constructed based on this principle has the ability to accurately simulate the dynamic response of actual buildings. Second, the form of simplified model of frame structure was derived, and the characteristics of the simplified model parameters were studied. Then, an iterative identification method for the parameters of the simplified model was proposed, which can identify all parameters of the simplified model by solely using a small number of wireless mobile sensors. Finally, a numerical simulation example of a 12-story 3-span steel frame structure was conducted, which investigates the predictive capability of the equivalent simplified model constructed by the method proposed herein to predict the dynamic responses of the actual frame structure subjected to different types of horizontal excitations, under the condition of without knowing the specific format of structural stiffness degradation and using only a small number of moving acceleration sensors. Simulation results show that the equivalent simplified model can very accurately predict the dynamic responses of the actual frame structure subjected to different types of horizontal excitations. Therefore, the model updating method for the equivalent simplified model of frame structures proposed herein will have important application potential in evaluating the structural safety and comfort of existing frame building structures under dynamic loads, such as wind and earthquake.