This article employs the multi-period difference-in-differences model to investigate the causal impact of innovative city construction on tourist destination competitiveness and its various dimensions based on panel data for 272 Chinese prefecture-level cities from 2005 to 2019. The findings indicate that innovative city construction significantly and positively impacts tourist destination competitiveness, with this effect growing over time. In particular, the impact on tourism industrial competitiveness is negative, whereas the effects on the competitiveness of tourism resources, ecological environment, and socio-economic support are positive and significant. The impact of innovative city construction on tourist destination competitiveness varies significantly across regions and administrative levels, with no variation found between the central and western regions. The possible mediating mechanisms include industrial structure, science and technology innovation, and environmental regulation. This article significantly contributes to the theoretical expansion of tourist destination competitiveness and its change mechanisms under innovative city construction.