In order to explore the design strategy of participatory design approach in the design of external human-machine interface (eHMI), this paper at the theoretical level researches the relevant literature and typical interfaces of eHMIs, and sorts out the basic concepts of explicit human-vehicle interaction features theory. Through the user participatory design method, we summarized the key design points of the eHMI and produced a design prototype, and optimized the prototype according to the participatory design experimental results and actual needs to obtain a design solution. The design was tested and evaluated at the practical level, and a strategy for user participation in the design of the external human-machine interface was concluded. The results show that the participatory design approach can improve the usability and acceptance of eHMIs, reduce the cognitive differences in the presentation of interface content, and provide a reference for the design of out-of-vehicle HCI in future work.