A method for determining topology of a packet transport network, PTN, the method implemented by a computer, the method comprising: dividing, according to rate levels for transmitting data V1, ···, Vn of links of the PTN, all of the links of the PTN into link sets L, ···, L(Vn), wherein n is a positive integer equal to or larger than 1; dividing, according to connection relationships of the links, a link set L(Vx) into link subsets L(Vx)1, ···, L(Vx)k, wherein 1≤x≤ n and k is a positive integer equal to or larger than 1; determining a network layer to which a link subset L(Vx)y is attributed, wherein 1≤ y≤ k; and outputting, topology information of the PTN, wherein the topology information comprises a ring forming ratio; wherein the method further comprises: before the determining a network layer to which the link subset L(Vx)y is attributed, labeling, according to network feature information, network layers to which nodes and/or links in the network are attributed, wherein the network feature information is used to characterize relations between the nodes and/or links and the network layers; after the dividing, according to the connection relationships of the links, a link set L(Vx) into link subsets L(Vx)1,..., L(Vx)k, determining a network type to which the link subset L(Vx)y is attributed; and after the determining a network layer to which a link subset L(Vx)y is attributed and the determining a network type to which the link subset L(Vx)y is attributed or re-determining the network type to which the link subset L(Vx)y is attributed, calculating the ring forming ratio of each network layer of the network, wherein the ring forming ratio of each network layer is a ratio between a number of nodes forming a ring in each network layer and a number of all nodes in said each network layer, the nodes forming a ring are nodes on a predetermined network type, and the predetermined network type comprises one of: a mesh network, a ring network, an intersecting ring network or a tangent ring network. dividing, according to rate levels for transmitting data V1, ···, Vn of links of the PTN, all of the links of the PTN into link sets L, ···, L(Vn), wherein n is a positive integer equal to or larger than 1; dividing, according to connection relationships of the links, a link set L(Vx) into link subsets L(Vx)1, ···, L(Vx)k, wherein 1≤x≤ n and k is a positive integer equal to or larger than 1; determining a network layer to which a link subset L(Vx)y is attributed, wherein 1≤ y≤ k; and outputting, topology information of the PTN, wherein the topology information comprises a ring forming ratio; wherein the method further comprises: before the determining a network layer to which the link subset L(Vx)y is attributed, labeling, according to network feature information, network layers to which nodes and/or links in the network are attributed, wherein the network feature information is used to characterize relations between the nodes and/or links and the network layers; after the dividing, according to the connection relationships of the links, a link set L(Vx) into link subsets L(Vx)1,..., L(Vx)k, determining a network type to which the link subset L(Vx)y is attributed; and after the determining a network layer to which a link subset L(Vx)y is attributed and the determining a network type to which the link subset L(Vx)y is attributed or re-determining the network type to which the link subset L(Vx)y is attributed, calculating the ring forming ratio of each network layer of the network, wherein the ring forming ratio of each network layer is a ratio between a number of nodes forming a ring in each network layer and a number of all nodes in said each network layer, the nodes forming a ring are nodes on a predetermined network type, and the predetermined network type comprises one of: a mesh network, a ring network, an intersecting ring network or a tangent ring network. before the determining a network layer to which the link subset L(Vx)y is attributed, labeling, according to network feature information, network layers to which nodes and/or links in the network are attributed, wherein the network feature information is used to characterize relations between the nodes and/or links and the network layers; after the dividing, according to the connection relationships of the links, a link set L(Vx) into link subsets L(Vx)1,..., L(Vx)k, determining a network type to which the link subset L(Vx)y is attributed; and after the determining a network layer to which a link subset L(Vx)y is attributed and the determining a network type to which the link subset L(Vx)y is attributed or re-determining the network type to which the link subset L(Vx)y is attributed, calculating the ring forming ratio of each network layer of the network, wherein the ring forming ratio of each network layer is a ratio between a number of nodes forming a ring in each network layer and a number of all nodes in said each network layer, the nodes forming a ring are nodes on a predetermined network type, and the predetermined network type comprises one of: a mesh network, a ring network, an intersecting ring network or a tangent ring network.