Urban blue-green space constitutes the ecological background of high-density urban areas, as part of the city’s public open space, maintaining the urban ecosystem service function and urban vitality, is an breakthrough point to the current construction of park cities and high-quality urban development. In view of the bottleneck problem that blue and green spaces are divided and worked separately in past urban construction, it is difficult to release the potential of the coupled development of blue and green spaces. The study constructs the basic characteristics of urban blue and green spaces and the evaluation index system of the coupling relationship and selects 130 blue and green spaces in the Changning District of Shanghai to conduct empirical research. The spatial and temporal distribution characteristics of blue-green spatial vitality in Changning District are elucidated by comprehensively adopting LBS big data, field surveys, and statistical analyses. Through the correlation study of the basic characteristics of blue-green spaces, the indicators of blue-green space coupling relationship, and the vitality of blue-green spaces, the key indicators of urban blue-green space characteristics that affect the vitality are revealed. The results show that: (1) There is a significant promotion effect of water bodies on the high vitality of urban blue-green space. (2) The vitality of blue-green space with water bodies has specific seasonal change characteristics. (3) The length of the blue-green boundary, the shape index of the blue-green boundary, and the area of the water body surrounded by the green space are the key factors to promote the vitality of the blue-green space, and the degree of blue-green fragmentation harms the vitality of the blue-green space. (4) In the small-scaled urban blue-green spaces, the blue-green coupling relationship significantly affects vitality. The study’s conclusions provide a theoretical basis and technical support for “blue-green integrated development” in the context of park city construction and urban quality development from the perspective of vitality enhancement.