To alleviate the contradiction between high-density urban spatial environments and high-frequency citizens’ activities, it is vital to determine the degree of openness of waterfront space, figure out the matching relationship between spatial openness and vitality intensity, identify imbalanced spatial zones and divide the order of intervention, and compensate for the limitations of subjective judgment in traditional planning decisions. This paper uses the Changsha Xiangjiang River waterfront space as a research sample based on multi-source data. It constructs the evaluation indicators system and research framework for the degree of openness of waterfront space. Then, by evaluating the openness and vitality intensity of the waterfront space and adopting the quadrant division method, waterfront space zones with a mismatched openness and vitality intensity were identified. Finally, planning interventions are prioritized based on a priority index. The results show the following: (1) The openness and vitality of the waterfront space of Xiangjiang River show the spatial distribution characteristics of “high in the middle and low in the north and south” and “high on the east bank and low on the west bank”. (2) Fifteen low-quality waterfront spatial zones with “low vitality intensity and low openness” and one with a severe imbalance of “low openness–high vitality intensity” were identified. These waterfront spatial zones cannot meet the requirements for the high-quality development of waterfront space. (3) The study delineates five priority levels for planning interventions. Among them, three waterfront space zones belong to priority V, mainly distributed north and south of the Xiangjiang River. Five waterfront spatial zones belonging to priority IV are concentrated in the middle of the Xiangjiang River. The above areas need to be prioritized for improvement to accurately promote the overall balanced development of the waterfront space.