Hibiya Park, known as Tokyo’s central park, is the progenitor of Japan’s modern parks and has undergone more than a century of development. Taking Hibiya Park as an example, this paper explores the real-life role of Japan’s historic urban parks as important urban public spaces that have assumed and complemented basic urban functions during their century-long development, as well as the implications for the context of sustainable urban park development, through combing historical data and field interviews. The study concludes that as urban public infrastructures, urban parks have assumed the role of complementing and improving urban functions in terms of social, living, disaster prevention, and ecological structures; at the same time, as important carriers of urban history, culture, and regional heritage, the way of evaluating their creativity and the protection of laws are important influencing factors for the sustainable development of urban parks.