Disclosed are a flow classifier, policy and charging rules function unit and controller. The flow classifier receives a service chain selection control policy sent by a policy and charging rules function unit. The service chain selection control policy includes a corresponding relation between an application type and an identifier of a service chain. The service chain is a path formed by a forwarding device and a value-added service device both of which a service flow with the application type needs to pass through. The flow classifier detects the service flow with the application type based on the service chain selection control policy and adds the identifier of the service chain to a message of the service flow. The flow classifier sends the message of the service flow with the added identifier of the service chain to a forwarding device directly connected to the flow classifier.