A method for establishing multicast service connections or for increasing multicast service receiving ends in an automatic switched optical network, the method comprising the steps of: sending (300, 500) a request for establishing a multicast service for a plurality of multicast service receiving ends (Z1-Z4) or for increasing at least one multicast service receiving end, respectively from a multicast service sending end to a connection controller; generating (304, 504) a multicast route inquiry request according to the multicast service sending end and the plurality of multicast service receiving ends (Z1-Z4) in the request for establishing the multicast service or according to the multicast service sending end and the increased at least one multicast service receiving ends in the request for increasing at least one multicast service receiving end, respectively, the multicast route inquiry request comprising the multicast service sending end and either the plurality of multicast service receiving ends (Z1-Z4) or the increased at least one multicast service receiving end, respectively, and the service type of the request being identified as multicast; sending (306, 506) the multicast route inquiry request to a route controller; inquiring (308, 508) a routing database according to the multicast route inquiry request on the route controller to acquire multicast route inquiry results; transferring the multicast route inquiry results to the connection controller; and establishing (312, 512), by the connection controller, connections of the multicast service sending end to each of the plurality of multicast service receiving ends (Z1-Z4) or to each of the increased at least one multicast service receiving ends, respectively, in turn according to the inquired multicast route inquiry results, wherein the step of inquiring (308, 508) the routing database comprises inquiring the routing database in terms of the principle that the multicast service should share connection resources; if the step of inquiring the routing database failed, sending the fail information to the connection controller; wherein the step of inquiring (308, 508) the routing database comprising inquiring the routing database in terms of the principle that the connection to at least one increased receiving end should share an existing multicast tree resource. sending (300, 500) a request for establishing a multicast service for a plurality of multicast service receiving ends (Z1-Z4) or for increasing at least one multicast service receiving end, respectively from a multicast service sending end to a connection controller; generating (304, 504) a multicast route inquiry request according to the multicast service sending end and the plurality of multicast service receiving ends (Z1-Z4) in the request for establishing the multicast service or according to the multicast service sending end and the increased at least one multicast service receiving ends in the request for increasing at least one multicast service receiving end, respectively, the multicast route inquiry request comprising the multicast service sending end and either the plurality of multicast service receiving ends (Z1-Z4) or the increased at least one multicast service receiving end, respectively, and the service type of the request being identified as multicast; sending (306, 506) the multicast route inquiry request to a route controller; inquiring (308, 508) a routing database according to the multicast route inquiry request on the route controller to acquire multicast route inquiry results; transferring the multicast route inquiry results to the connection controller; and establishing (312, 512), by the connection controller, connections of the multicast service sending end to each of the plurality of multicast service receiving ends (Z1-Z4) or to each of the increased at least one multicast service receiving ends, respectively, in turn according to the inquired multicast route inquiry results, wherein the step of inquiring (308, 508) the routing database comprises inquiring the routing database in terms of the principle that the multicast service should share connection resources; if the step of inquiring the routing database failed, sending the fail information to the connection controller; wherein the step of inquiring (308, 508) the routing database comprising inquiring the routing database in terms of the principle that the connection to at least one increased receiving end should share an existing multicast tree resource.