Network address translation (NAT) traversal is a critical technology for real-time video streaming between two endpoints. The port predictive algorithm of the NAT mapping rule is the core of NAT traversal. However, most port predictive algorithms in the NAT traversal method are too simple or unclear. The behavior of NAT port mapping in devices in real network environments is complex and cannot be accurately predicted. In this study, NAT port mapping behavior was examined and a mathematical model was established to enhance the port predictability of NAT and increase the success rate of NAT traversal.