Urban green spaces (UGSs) are closely to residents’ physical and mental health, but rapid urbanization has significantly changed the spatial pattern of UGSs exposure. With the development of social economy, the meaning of urbanization has changed from a single-dimensional demographic indicator to a multi-dimensional concept containing demographic, economic, land, socioeconomic indicators. Although some existing studies have focused on the measurement methods, spatio-temporal characteristics and influencing factors of UGSs exposure, it is still necessary to further explore the influence mechanism of urbanization on UGSs exposure from the perspective of multi-dimensional urbanization. Therefore, the population-weighted UGSs exposure index was firstly used to analyze the spatio-temporal differences of UGSs exposure in the Yangtze River Economic Belt. Secondly, by constructing multi-dimensional urbanization indicators, the geographical detector model and geographically weighted regression model were used to identify the dominant impacting factors and explore their spatio-temporal heterogeneity impacts on the UGSs exposure. Finally, the influencing mechanism of multi-dimensional urbanization on spatio-temporal exposure of UGSs was further analyzed. The results showed that: (1) The level of UGSs exposure in the Yangtze River Economic Belt showed a trend of ‘increasing first and then decreasing’, but the overall value of UGSs exposure has improved. The spatial differences of UGSs exposure were also obvious: middle reaches > upper reaches > lower reaches. Moreover, the cities with slow urbanization and abundant green paces resources tended to have a higher level of UGSs exposure. (2) From 2005 to 2018, green space coverage, PM2.5, built-up area, gross domestic product, and elevation have always been the dominant factors for the spatial differences of UGSs exposure. The synergistic effect between green space coverage and other factors on the spatial differences UGSs exposure was significantly stronger than its individual effect. Meanwhile, the synergistic effect between built-up area, gross domestic product and other factors on the spatial differences UGSs exposure gradually also increased with time. (3) The influence of all dominant factors had obviously spatio-temporal heterogeneity. Overall, green space coverage had stably positive impact on UGSs exposure. From 2005 to 2018, the negative impact of economic development on UGSs exposure gradually covered all cities, while the positive impact of ecological improvement and urban sprawl on UGSs exposure were gradually significant. This study has deeply analyzed the influence mechanism of urbanization factors on the spatial and temporal pattern of UGSs exposure, and the results are helpful to optimize the layout of UGSs and coordinate the development of multi-dimensional urbanization to improve the residents’ living environment.