The reliability of the Internet of Things (IoT) system is analyzed and studied through ordered binary decision diagram (OBDD) to improve its design, application, and development. Based on the OBDD analysis, a reliability evaluation method named as enhanced node expansion (ENE) is proposed. This method provides an effective solution for the reliability assessment of IoT with large scale and complex network structure. A link importance assessment method based on OBDD analysis is also established. The proposed method can accurately and effectively evaluate the reliability of the IoT network and is practical for discussing the reliability, design, and development of this system.