The invention discloses a path calculation method and system, and relates to the technical field of communication. The path calculation method is applied to a wavelength switched optical network (WSON), and comprises the following steps: receiving a plurality of path calculation requests, grouping all the path calculation requests, and calculating K shortest paths from a source node of each group to a sink node of the group, wherein each group is provided with a source node and a destination node, and the wavelength channels of the K shortest paths in each group are used for meeting the path calculation request of the group; in all the K shortest paths, performing path segmentation by taking the relay node as a segmentation point, and storing the sub-paths conforming to the resource constraint into a sub-path set; constructing a linear programming model based on all the K shortest paths and the resource constraints, and determining an optimal path set meeting the most path calculation requests according to the linear programming model. According to the invention, under the condition that network resources are limited, more reachable paths are calculated so as to recover more services.