With the rise of the digital age, Internet of Things (IoT) technology is now widely used in many industries, particularly in smart cities and energy management. This paper looks into how IoT-based Intelligent Energy Management Systems (IEMS) are used in digital cities. It focuses on how they can improve energy efficiency, better manage resources, and support environmental sustainability. The study examines the current state, technical structure, and challenges of IEMS, using real-world examples. At the same time, a multi-level data analysis framework is suggested to enhance data handling and real-time response, allowing for more precise energy optimization. The experiment shows large energy savings, with a 20% drop in electricity use during peak hours and around 12% savings throughout the day. To promote IEMS in cities, the study suggests several changes. These include improving IoT device compatibility, boosting edge computing, and refining data algorithms. The goal is to support sustainable city development.