A load balancing routing method for networks is disclosed. The routing method includes following steps. A network topology graph and a plurality of expected bandwidth demands corresponding to a plurality of source-destination pairs are received by a network server. A plurality of link criticalities of a plurality of links established according to the source-destination pairs is calculated by the network server according to the network topology graph and the expected bandwidth demands. A plurality of expected loads of the links is calculated by the network server according to the link criticalities. A plurality of cost values is calculated according to a plurality of residual capacities of the links and the corresponding expected loads. A better transmission path corresponding to each of the source-destination pairs is selected by the network server according to the weighted sum of the cost values corresponding to the links in the source-destination pair.