The key problem of wavelen gth division multiplexing (WDM) optical network is the routing and wavelength assignment (RWA) problem which has the objective to minimize the bloc king probability of the whole network.But the phenomenon of heavy-load over some particular links,which results from the unbalance of the network structure,may bring to high blocking probability.Therefore a link bl ocking probability model is proposed based on the Erlang loss formula in this paper.Then an optimization model is established to m aximize the route unblocking probability.The idea of decomposition coordination is utilized in o rder to overcome the nonlinearity by setting the link load and converting the original problem to a shortest path problem.Ev entually,a similar Dijkstra algorithm,which is combined with the updating of link load,is designed to iteratively solve the sho rtest path problem.Simulation results show that the proposed algorithm can approximately solve the original optimization pr oblem and at most reduce blocking probability by 27.6% compared with the shortest path (SP) algorithm and LBF R algorithm.So the proposed algorithm can efficiently balance the load of the whole network,get the network cong estion reduced and finally improve the transmission performance.