Urban green space (UGS) is crucial for urban sustainability, yet equity in access to urban green space remains a global challenge amidst rapid urbanization. Guangzhou, a megacity in China’s Pearl River Delta, exemplifies this challenge, with its population increasing from 5.9 million in 1990 to 18.7 million in 2020, leading to intensified land use conflicts. This study analyzes the changes in urban green space across three strategic zones—Old Guangzhou, New Guangzhou, and Future Guangzhou—compared to other areas, and equity over time using land use transfer matrices, landscape indices, hotspot analysis, and the Gini coefficient. It also explores the driving factors behind these changes. The results show a 16% decline in total UGS area from 1990 to 2020, with fragmentation peaking between 2000 and 2010, as indicated by a 24% increase in patch density and an 18% decrease in connectivity; growing spatial inequity, with the overall Gini coefficient rising over time—Old Guangzhou exhibited severe inequality (0.806) due to the scarcity of community-level urban green space, while Future Guangzhou demonstrated a relatively balanced distribution (0.523); and a shift in policy focus from basic greening to ecological prioritization after 2010, which slowed UGS loss but failed to address the disparities between core and peripheral areas. These findings are significant not only for Guangzhou but also reflect broader global issues faced by urban areas undergoing rapid urbanization. This study provides a comprehensive framework for balancing urban growth with equity, offering valuable insights for rapidly urbanizing regions worldwide.