Although neglected in previous studies, tourist-to-tourist interaction (TTI) is a core part of festival experience. It is widely acknowledged that interactions between tourists significantly influence behavioral reactions such as desire to stay, satisfaction, and loyalty, which are important for tourism destination marketing. This study used grounded theory to obtain insights into onsite interactions between tourists and to propose a conceptual model of TTI on the Midi Music Festival in China. The model constitutes the types, drivers, and influence of TTI. Compared with mutual assistance and conflict, entertainment interaction plays an essential role in the overall evaluation of the festival experience. Individual characteristics are the internal drivers of interactions between tourists. Environmental elements including the festivalscape and social festivalscape are influential exogenous factors. Additionally, spatial locations of tourists at the venue play mediating roles between the driving elements and TTI. Since entertainment incidents construct the essential part of onsite interactions at festivals, managers can shape the atmosphere to encourage tourists to engage in interactive entertainment with others tourists. This should improve participants’ overall evaluations of the festival experience as well as the sustainable development of destinations where festivals are held.