A method for joint optimization of routing path selection and content server selection in a communication network including a plurality of content providing servers, wherein the communication network comprises a plurality of sub-networks, and the joint optimization is performed in parallel in each sub-network of the plurality of sub-networks, the method comprising: obtaining link information, server and bandwidth information, and user requirement information of a sub-network, wherein the server and bandwidth information comprises virtual server bandwidth of every external port of the sub-network, and the virtual server bandwidth of a given external port of the sub-network is bandwidth of a server off said given external port of the sub-network, wherein the bandwidth of the server off said given external port of the sub-network is required by the sub-network through said given external port, the server off said given external port of the sub-network is considered as a virtual server located on a device at the ingress of the sub-network, and the virtual server bandwidth of said given external port of the sub-network is the smallest one selected from the sum of bandwidth that can be provided by all servers in an adjacent sub-network connected to said given external port of the sub-network, the maximum egress bandwidth of the adjacent sub-network through said given external port and the maximum ingress bandwidth of the sub-network through said given external port; obtaining an optimal routing parameter and a server selection parameter of the sub-network according to the link information, the server and bandwidth information, and the user requirement information; obtaining optimized ingress bandwidth of every external port of the sub-network according to the optimal routing parameter and the server selection parameter; and comparing the optimized ingress bandwidth and the virtual server bandwidth of every external port, and if results of the comparison between the optimized ingress bandwidth and the virtual server bandwidth of all external ports are smaller than a set error value, applying the optimal routing parameter and the server selection parameter in the sub-network; wherein the server and bandwidth information further comprises at least one of the following: a set of servers in the sub-network and bandwidth that can be provided by each of said servers. obtaining link information, server and bandwidth information, and user requirement information of a sub-network, wherein the server and bandwidth information comprises virtual server bandwidth of every external port of the sub-network, and the virtual server bandwidth of a given external port of the sub-network is bandwidth of a server off said given external port of the sub-network, wherein the bandwidth of the server off said given external port of the sub-network is required by the sub-network through said given external port, the server off said given external port of the sub-network is considered as a virtual server located on a device at the ingress of the sub-network, and the virtual server bandwidth of said given external port of the sub-network is the smallest one selected from the sum of bandwidth that can be provided by all servers in an adjacent sub-network connected to said given external port of the sub-network, the maximum egress bandwidth of the adjacent sub-network through said given external port and the maximum ingress bandwidth of the sub-network through said given external port; obtaining an optimal routing parameter and a server selection parameter of the sub-network according to the link information, the server and bandwidth information, and the user requirement information; obtaining optimized ingress bandwidth of every external port of the sub-network according to the optimal routing parameter and the server selection parameter; and comparing the optimized ingress bandwidth and the virtual server bandwidth of every external port, and if results of the comparison between the optimized ingress bandwidth and the virtual server bandwidth of all external ports are smaller than a set error value, applying the optimal routing parameter and the server selection parameter in the sub-network; wherein the server and bandwidth information further comprises at least one of the following: a set of servers in the sub-network and bandwidth that can be provided by each of said servers. a set of servers in the sub-network and bandwidth that can be provided by each of said servers.