Due to the impact of the new crown epidemic, people’s online services have increased. Among them, online education, online conferences and other services have higher requirements on network delay and jitter. Therefore, based on the software defined network (SDN) architecture, this paper designs a real-time transmission scheme using the programming protocol-independent packet processors (P4) language in the programmable data plane. The scheme is based on a variable threshold mechanism and establishes a threshold feedback self-adjustment mechanism on the programmable data plane, so that priority scheduling and rerouting scheduling can adapt to network fluctuations and reduce latency. The experimental results show that the improved scheme has obvious improvements in delay and jitter, and improves the quality of real-time transmission services.