Urban parks and public transport are indispensable elements of a compact megacity for their environmental and social values. However, few measures of urban park accessibility have considered the public transport travel mode. Based on the framework of geographic information systems (GIS) network analysis, this study proposes an innovative method to incorporate public transport travel mode into urban park accessibility evaluations. Taking Shanghai, China, as the study area, we measured home to park and park from home travel times on multi-modal transport networks, calculated the accessibilities by multiple equations, and compared accessibilities for different districts. These methods extend current accessibility measures by calculating accessibility at a realistic level, and provide a measure of public transport service for urban parks. The results for Shanghai show that approximately 99.95% of home to park routes might include public transport. The distribution of home to park public transport accessibility of the city was uneven. The patches with best accessibility tend to be distributed in the built-up area in the city centre. Public transport access to urban parks is inhomogeneous for different districts, because of urban park locations, road network characteristics, and uneven public transport supply. The distribution of park from home public transport accessibility has no significant correlation with district development stage. Public transport service in Shanghai takes no account of the factors of park star rating or size. Positive actions are required to improve the equity of public transport access to the important public health resources of urban parks.