A dynamic platoon formation method under a mixed autonomous vehicles flow is provided. The method implements dynamic platooning by taking into account a fact that a traffic flow is a mixture of HDVs and CAVs. The dynamic platoon formation method includes: selecting lanes as candidate lanes in turn; constructing a decision tree from a current moment to a moment of platoon formation according to the following process: constructing a decision space for each CAV, generating a compatible decision set, selecting and executing a compatible decision, and updating location and speed information of all vehicles; and selecting, according to a predetermined index (including TTP and DTP), an optimal decision sequence as a decision sequence corresponding to the candidate lane.