With a growing number of user-side heterogeneous power Internet of Thing devices (UPIDs) integrating into power systems, a cyber attack on UPIDs will cause serious damage. Hence, the network security risk assessment of UPIDs is a key problem that needs to be solved urgently. First, taking into account the network security protection measures deployed on the terminal, mobile application and cloud of UPIDs and the operational characteristic of the terminal, this paper constructs a network security risk indicators system of UPIDs. The indicator weights are calculated by the proposed method based on improved analytic hierarchy process and the variation coefficient of indicators. A network security risk assessment model of UPIDs is designed based on the network security vulnerability and the potential impact of UPIDs on the power system under malicious control. Finally, indicator benchmarking is introduced to analyze the weak links of the network security protection measures of components such as current terminal, mobile application and cloud terminal, and the corresponding improvement direction is pointed out. The research is expected to provide an effective scientific criterion for the construction and implementation of the user-side power Internet of Things, so as to reduce the network security risk on the user-side and ensure the operation of power systems.