The invention discloses a convergence type metropolitan area wavelength division access network system and an accessing method, and relates to the field of metropolitan area access. The system comprises an OLT located in a central apparatus room, m ROADM nodes and n far-end OTUs, wherein m and n belong to positive integers, m is larger than or equal to 1, and n is larger than or equal to m. The central apparatus room is a network convergence point, the OLT of the central apparatus room and the m ROADM nodes are sequentially connected through optical fibers to form an annular topological structure, the connecting direction of the m ROADM nodes in an annular topology is expressed in the eastward direction and the westward direction, on the basis of the clockwise direction, the eastward direction of a prior ROADM node is connected with the westward direction of a next ROADM node, only one optical fiber exists between every two adjacent ROADM nodes, and each ROADM node is connected with at least one far-end OTU. All services of a service provider can be accessed through one network, the robustness requirements such as mobile backhaul and a special line for a big customer are met, management is convenient, cost is low, bandwidth is allocated flexibly, capacity is large, and the accessing distance is long.