Abstract: A tranquil environment is restorative, and can relieve people’s stress in daily life. The human body mainly perceives the degree of external tranquility through the sensory (auditory and visual) organs. Studies have shown that green space can enhance tranquility and thus contributes to the improvement of urban environment and human health. The border areas of park green space lie in the transition belts between urban areas and park green space, subject to traffic noise and urban architectural vision. To enhance the tranquility of the border areas of park green space and explore the relations of plant composition and tranquil environment, this paper takes six greenbelts of three urban parks in Beijing as the research objects. First, it introduces the Tranquility Rating Prediction Tool(TRAPT) to have a comprehensive and quantitative evaluation of the tranquility of the green space boundary areas of the parks in the visual and auditory angles. Second, it verifies the TRAPT model by taking a sample survey of subjective feelings of park visitors, and gets a preliminary strategy for the optimization and upgrading of the urban tranquil environment boundary communities.