A method for flow measurement, comprising: receiving, by a forwarding device, a data flow, and obtaining matching information of the data flow; searching, by the forwarding device, a flow table by using the matching information, and if no information that is consistent with the matching information exists in the flow table, sending the data flow to a controller; receiving, by the forwarding device, packet header information and operation information of the data flow that are sent by the controller, and writing the packet header information and operation information into the flow table, wherein the operation information contains at least a measurement operation for a feature identifier, wherein the feature identifier is used as a measurement item identifier which enables the forwarding device to measure the data flow for the feature identifier; searching, by the forwarding device, a measurement instance table according to the feature identifier in the measurement operation, wherein the measurement instance table records a feature identifier of a sent data flow and its corresponding traffic information; if a first feature identifier is recorded in the measurement instance table and the first feature identifier is consistent with the feature identifier, updating, by the forwarding device, in the flow table and according to an index of an entry corresponding to the first feature identifier in the measurement instance table, the measurement operation for the feature identifier to a measurement operation for the index; and executing, by the forwarding device, various operations in the operation information in the flow table, and when executing a measurement operation in the operation information in the flow table, updating traffic information corresponding to the first feature identifier recorded in the measurement instance table. receiving, by a forwarding device, a data flow, and obtaining matching information of the data flow; searching, by the forwarding device, a flow table by using the matching information, and if no information that is consistent with the matching information exists in the flow table, sending the data flow to a controller; receiving, by the forwarding device, packet header information and operation information of the data flow that are sent by the controller, and writing the packet header information and operation information into the flow table, wherein the operation information contains at least a measurement operation for a feature identifier, wherein the feature identifier is used as a measurement item identifier which enables the forwarding device to measure the data flow for the feature identifier; searching, by the forwarding device, a measurement instance table according to the feature identifier in the measurement operation, wherein the measurement instance table records a feature identifier of a sent data flow and its corresponding traffic information; if a first feature identifier is recorded in the measurement instance table and the first feature identifier is consistent with the feature identifier, updating, by the forwarding device, in the flow table and according to an index of an entry corresponding to the first feature identifier in the measurement instance table, the measurement operation for the feature identifier to a measurement operation for the index; and executing, by the forwarding device, various operations in the operation information in the flow table, and when executing a measurement operation in the operation information in the flow table, updating traffic information corresponding to the first feature identifier recorded in the measurement instance table.