This paper investigates the diverse routing in a wavelength division multiplexing (WDM)-based optical network under SRLG-disjoint constraints. In operational optical networks there are a lot of traffic flows within every lightpath. Any failure of one Iightpath will lead to a great loss. So we should provide path protection for the working lightpath. The concept of Shared Risk Link Groups (SRLG) is introduced in optical networks by IETF, which is defined as a group of links that share a common risk component whose failure can potentially cause the failure of all the links in the group. This concept groups all of the entities, such as wavelengths and links, etc., that are affected by a single failure. Now when path protection is employed, for any lightpath connection request, we compute two SRLG-disjoint lightpaths, one as working path and the other as protection path. There are some literatures, which propose methods for link-disjoint paths pair or node-disjoint paths pair, but few algorithms for SRLG-disjoint paths pair. The SRLG-disjoint constraints entail the general constraint-based path computation algorithms. Since this problem is an NIP-complete problem and there is no algorithm which could be used to solve this path computation in polynomial time. This paper presents a heuristic algorithm, Low-cost Pair of SRLG-Disjoint Paths Algorithm (LPSD), to solve this problem. LPSD can compute two SRLG-Disjoint paths simultaneously, and the total cost of the two paths is near optimal. Analysis and simulation are also given out.