<p>In a mixed traffic environment consisting of connected and automated vehicles (CAVs) and human-driven vehicles (HDVs), effective platooning cooperation behavior is crucial for enhancing traffic safety and efficiency. The platooning process consists of two stages: platooning formation and platoon driving. In the formation of decision-making, the selection of interaction targets is indispensable. This study proposes a novel integrated co-opetition index (ICI) to assess the cooperation and competition behavior during the platooning process of CAVs and HDVs, which is applicable to optimizing CAV platooning strategies for HDVs in mixed traffic. First, using the Waymo dataset, cooperative movement features are extracted from same-lane and cross-lane platooning events between CAVs and HDVs. Four evaluation metrics are proposed based on the correlation of features: following intention index, lane change competition index, stable following index, and interaction friendliness index. An integrated co-opetition index (ICI) is then constructed to characterize the risks and benefits of the dynamic platooning process between CAVs and HDVs. Validation in various traffic scenarios shows that compared to the single-threshold indicator: time to collision, the composite-threshold indicator: surrogate safety measures, and game theory equilibrium point. ICI demonstrates significant advantages in platooning success rate, platooning efficiency, and traffic efficiency improvement. Under ICI guidance, the average platooning success rate increases by 5.84%, platooning efficiency improves by 14.4%, and traffic efficiency increases by 8.53%. ICI provides a comprehensive evaluation of HDV behavior, offering guidance for dynamic adjustments of CAV platooning strategies, making it more suitable for the design of CAV-HDVs interaction clustering decisions in mixed traffic environments.</p>