Communication techniques for Internet of Things (IoT) have attracted research attention because of the increasing number and variety of connected devices. The IoT systems are able to provide a variety of applications by collecting information from various 'things' using the network constructed by the things. The IoT systems are required to provide the applications in real-time. For example, the immediacy and the time restriction will be more important to the applications. Although there have been many applications of real-time IoT systems, a specific model for performance evaluation has not received adequate attention. Therefore, in this paper, we focus on the modeling aspect for evaluating the performance of real-time IoT system. Specifically, our proposed model is constructed by utilizing feedback control theory. In order to apply feedback control theory for our model, we introduce a method for representing the 'things' as the controlled objects in the control theory. After that, the overall system model of the real-time IoT with the controlled objects is represented. Finally, our represented method is validated through the numerical analysis while varying the parameters.