To mitigate pollution from transportation, the multimodal transport demonstration projects have been implemented in China since 2016. A research gap exists in investigating the impacts of multimodal transport on eco-efficiency of port cities. The eco-efficiency is the reflection of the environmental impact of the economic activities. This study evaluates these impacts by using difference-in-difference (DID) model and Spatial difference-in-difference (SDID) model. The results show that the implementation of multimodal transport demonstration projects can significantly improve the eco-efficiency of port cities and generate the spatial spillover effect to the nearly port cities.