Abstract: Under the backdrop of great transformation and development of China’s new urbanization, scientific understanding of the influencing mechanism of urban green space construction has become an important prerequisite for improving the quality of human settlement environment and realizing the green development of cities. By taking the transect of land-bridge passage as the research target with the geographical detector method, this paper explores the influencing mechanism of regional difference of the green rate of built district of 139 cities along the sample line from 1996 to 2016. The results show: 1) The green rate of built district along the transect has been increasing year by year, however with obvious differentiation in time and space, showing a U-shaped pattern high in the eastern and western ends and low in the middle; 2) Geographical detection shows that the difference of green rate of built district along the transect is the result of nonlinear or double-factor interactions of nature, economy and policy factors. The average annual temperature is the core leading factor, followed by the garden city policies and altitude elevation; 3)The natural geographical background is the major basis for the difference. The policy guidance is the key factor. Economic development is the direct driving force. The industrial structure, land supply and infrastructure are the external motive forces. This study has quantitatively presented the large-scale, long-term effects of natural factors on the difference of green space construction. It is also an attempt of typical areas and typical methods in the field of disciplines by detecting the comprehensive effects of the multi-dimensional factors of “natureeconomy-policy”, in order to more accurately measure the urban green space construction.