For reasons of survivability, many methods have been introduced to Automatically Switched Optical Network (ASON), such as path protection. In path protection, the protection path is risk-disjoint with the working path, which can improve the survivability of network. The complete risk-disjoint routing algorithm (CRDRA) is the most popular algorithm in protection path selection at present, in which the links sharing same risk with those contained in the working path are pruned away from the available resources when calculating protection path. By using this algorithm, the survivability of network can be enhanced; but the number of connections that can be successfully routed over current network drops. In this paper, a partial risk-disjoint routing algorithm (PRDRA) based on shared risk link group (SRLG) is proposed. In this algorithm, the risk-sharing links are not pruned away but had their weight adjusted to a proper value that is larger than normal value but still comparable. Selecting protection path with PRDRA, improved survivability can be achieved while the number of connections that can be successfully routed over current network is kept from serious decline. Routing simulations have been done over mesh networks to compare the two different algorithms. With the simulation results, a conclusion can be made on the performance of different algorithms.