Abstract: Multipath routing is an effective technique to improve the reliability and robustness of Internet, while what strategy should be taken by the routing data plane as the grounds for data retransmission is the core problem in multipath routing. To solve the problem that the Internet traffic in many applications is so sensitive to the packet loss rate, a linear smoothing process is used to predict the packet loss rate in multipath network, based on the prediction practice in combination with the theory of optimization. Then, the predicted packet loss rate is taken as the precondition for PSO so as to take the optimal solution which makes the system average packet loss rate minimal as the grounds for the retransmission ratio of multipath data. Simulation results demonstrated that the proposed scheme is available to decrease the packet loss rate in multipath network more efficiently than other techniques such as the shortest path routing or equal splitting among multipath routings.