A method for Deep Packet Inspection, DPI, control, comprising: sending (S10, S20), by a device for DPI control, a traffic collection request to a network controller via a northbound interface of the network controller according to a pre-set collection policy, wherein the traffic collection request is configured to allow the network controller to parse and process to determine one or more network devices which need the traffic collection request and to send a request for traffic collection to the determined one or more network devices which need the traffic collection request, and wherein the traffic collection request is configured to specify traffic data to be collected via parameters that assign specific service flows from specific users and specific IP flows and traffics from specific ports that are to be collected; directly receiving (S11, S21), by the device for DPI control, the traffic data collected by the determined one or more network devices which need the traffic collection request without using the network controller; analyzing and processing (S12, S22), by the device for DPI control, the received traffic data from the determined one or more network devices which need the traffic collection request to generate each of network control policies corresponding to each of the determined one or more network devices which need the traffic collection request, wherein the network control policies describe application layer requirements; sending, by the device for DPI control, the network control policies to a network capacity control device; analyzing and processing, by the network capacity control device, the received network control policies, and converting the received network control policies into first network control policies that are recognizable by the network controller; sending, by the network capacity control device, the first network control policies to the network controller via the northbound interface of the network controller; analyzing and processing (S13, S23), by the network controller, the received first network control policies to determine one or more network devices which need the network control policies, and converting, by the network controller, the received first network control policies into second network control policies; sending (S13, S23), by the network controller, each of the second network control policies via the southbound interface of the network controller to a corresponding network device which is comprised in the determined one or more network devices which need the network control policies so as to implement the DPI control; and receiving (S14, S24), by the device for DPI control, feedback messages reported by the network controller, wherein the feedback messages are configured to indicate that the network devices have successfully executed the network control policies. sending (S10, S20), by a device for DPI control, a traffic collection request to a network controller via a northbound interface of the network controller according to a pre-set collection policy, wherein the traffic collection request is configured to allow the network controller to parse and process to determine one or more network devices which need the traffic collection request and to send a request for traffic collection to the determined one or more network devices which need the traffic collection request, and wherein the traffic collection request is configured to specify traffic data to be collected via parameters that assign specific service flows from specific users and specific IP flows and traffics from specific ports that are to be collected; directly receiving (S11, S21), by the device for DPI control, the traffic data collected by the determined one or more network devices which need the traffic collection request without using the network controller; analyzing and processing (S12, S22), by the device for DPI control, the received traffic data from the determined one or more network devices which need the traffic collection request to generate each of network control policies corresponding to each of the determined one or more network devices which need the traffic collection request, wherein the network control policies describe application layer requirements; sending, by the device for DPI control, the network control policies to a network capacity control device; analyzing and processing, by the network capacity control device, the received network control policies, and converting the received network control policies into first network control policies that are recognizable by the network controller; sending, by the network capacity control device, the first network control policies to the network controller via the northbound interface of the network controller; analyzing and processing (S13, S23), by the network controller, the received first network control policies to determine one or more network devices which need the network control policies, and converting, by the network controller, the received first network control policies into second network control policies; sending (S13, S23), by the network controller, each of the second network control policies via the southbound interface of the network controller to a corresponding network device which is comprised in the determined one or more network devices which need the network control policies so as to implement the DPI control; and receiving (S14, S24), by the device for DPI control, feedback messages reported by the network controller, wherein the feedback messages are configured to indicate that the network devices have successfully executed the network control policies.