As an integral component of urban systems, Urban Green Spaces (UGS) exhibit complex and multifaceted interactions with the overall system. Current studies mainly focused on UGS characteristics, paying less attention to their broader urban system patterns. Few studies explore the multi-dimensional features of UGS—such as scale, quality, and distribution—and their non-linear spatiotemporal relationships with urban populations, including count, age, and gender. Hence, from the perspective of complex systems, this study employs urban scaling theory to analyze the multi-dimensional scaling relationship evolution between UGS and population in Chinese cities using multi-source remote sensing and population data from 2000 to 2020. The characteristic calculations were performed, and further analysis was conducted to remove scale effects and identify the spatiotemporal patterns of UGS performance. Our results indicate that over the past 20 years, the relationship between UGS and population in Chinese cities has exhibited a consistently robust sub-linear scaling relationship, reflecting the economies of scale. The green space scaling exponent steadily increased from 0.497 to 0.614, yet it remains significantly below the theoretical value of 0.85, indicating a general insufficiency in the supply of UGS, particularly for the elderly population aged 60 and above. Notably, there are significant differences in scaling characteristics among cities with varying quality of green spaces, which deviate from the assumptions of urban scaling theory. The cities with the highest green space coverage exhibit the most pronounced economies of scale, whereas the scaling characteristics of cities with medium to high green biomass gradually converge. After accounting for the influence of scale effects, the overall performance of UGS in China has shown a steady upward trend, accompanied by a significant clustering distribution pattern. Specifically, the performance of green spaces increasingly exhibits a "high-high" clustering mode, particularly in the region extending from the North China Plain to the Yangtze River Delta. Our research confirms the widespread presence of sub-linear economies of scale in the evolution of UGS, as well as the spatiotemporal variations in scale economies and local performance among different populations and cities. In the context of deepening aging and urbanization, this study provides a decision-making basis for better meeting the needs of green space planning and construction in cities of varying scales and population structures, thereby supporting the achievement of sustainable urban development goals.