Carpooling, as an emerging travel mode, has not yet been paid sufficient attention despite its merits of convenience, cost-efficiency, and sustainability. The studies of carpooling, especially on the factors influencing carpooling, are inadequate. To tackle this problem, what and how the factors influence travelers' mode choice are studied with a practical trial. Based on a qualitative survey, we found that the travel time, travel cost, safety, punctuality, comfort, social contact, and identity promotion are potential influencing factors. Then a stated preference (SP) survey is conducted to address the main factors influencing carpooling. Finally, three key factors (travel time, travel cost, and safety) are singled out and the interaction of travel time and travel cost are explored by a binary logit regression analysis, respectively. Following the findings of the main factors and their interaction, related suggestions are proposed to promote the future application of carpooling.