According to the unbalanced traffic features and excessive data plane overhead faced by backbone routers, a novel Function migration algorithm (FMA) is proposed. Programmable routers (PRs) are used in FMA. With the router function migration model, PRs set and forward majority traffic through FMA link. Core routers obtain a simplicity function implementation. Theoretic analysis shows that FMA can reduce the forwarding burden and transmission delay. Simulations prove that FMA obtains a lower transmission delay and packet loss rate.