Abstract: The green space system occupies a significant place in all previous urban planning of Ottawa. It has had a profound impact on the capital's urban structure, spatial form, urban growth and residents’ lives. The paper studies Ottawa’s urban planning and green space planning in the past century, analyzes the three major phases of green space system development, including the park system planning to enhance the image of the capital in the early 20th century, the national capital planning mainly to curb urban growth in 1950, and the comprehensive and special planning for nature conservation, recreation and agriculture in the past 20 years, and ultimately elaborates on the formation and development of Ottawa’s green space system in different times. By analyzing the planning backgrounds, goals and strategies of different stages, the paper summarizes experience and characteristics in its development and transformation process, to provide reference for the construction of green space system in China.