Public data is an important resource for the development of city clusters, and assessing the impact of public data opening on the competitiveness of city clusters provides theoretical support for the collaborative development of city clusters. This paper conducts an empirical analysis based on the panel data of 11 national-level city clusters in China from 2012 to 2022 to test whether public data openness can promote the competitiveness of city clusters. It is found that public data openness can significantly improve the regional competitiveness of city clusters. Heterogeneity analysis shows that in city clusters with a lower level of intelligentization construction, public data openness helps to improve the competitiveness of city clusters; when the degree of cultural segmentation within city clusters increases, the effect of public data openness on the improvement of the competitiveness of city clusters will be weakened. Through empirical analysis, this paper evaluates the practical value of public data openness on the development of city cluster competitiveness, which is of practical significance for promoting public data openness and sharing and stimulating the potential of data elements.