The main urban area of Jinan is taken as the research area, and the hexagon converged residential area of 300 m side length is taken as the research unit. Using the multistage radius Gaussian two-step mobile search method, the paper analyzes the temporal and spatial characteristics of the walking accessibility of different levels of park green space and the comprehensive accessibility of park green space in 2010 and 2021. The factors influencing the spatial differentiation of the accessibility of green space in parks are explored by means of geographic detectors. The results show that: (1) From 2010 to 2021, the average accessibility of green space in three levels of parks in the main urban area of Jinan has increased, and the average accessibility of Grade I park green spaces is the highest and the improvement is the greatest. The spatial pattern of accessibility of green space in Grade I parks has increased by “ribbon” layout on the basis of the original “core-cluster”. The accessibility of green space in Grade II and Grade III parks is “cluster-like” and “scattered”, respectively. (2) The average comprehensive accessibility of park green space in the main urban area of Jinan increased from 42.94% in 2010 to 59.53% in 2021, and the spatial pattern and evolution of comprehensive accessibility showed similar characteristics to Grade I park green space, and the phenomenon of “cluster diffusion” in the eastern part of the main urban area was consistent with the direction of urban construction. (3) The spatial pattern of the accessibility of park green space is comprehensively affected by four aspects of “supply - connection - demand - social economy”. The influencing factors of the accessibility of different levels of park green space are similar, but the influence intensity of each factor is significantly different. Besides, the difference of influence intensity increases with the decline of park green space grade.