In the past 30 years, China has experienced development at full speed, andthe cities have expanded rapidly. There have been dozens of megacitieswith millions of people. Due to the lack of preparation of various factors,these cities will inevitably also have some urban diseases similar to thosein the mega-cities of the world. How to develop mega-cities, especiallyhow to ensure the sustainable development of mega-cities, such as Beijing, Shanghai, Guangzhou, etc., is a question that must be answered. Thispaper mainly discusses the challenges faced with city planning, especiallyfor mega-cities, taking Beijing as an example and analyzes from following aspects: institutional challenges, demographic challenges, and environmental challenges, and hopes to provide references for city planners