IP Switching is a new routing technology Proposed to improve the Performance of IP routers. Flow classification is one of the key issues in IP Switching. To achieve better performance, flow classification should be matched to the varying IP traffic and an IP switch should make use of its hardware switching resources as fully as possible. This paper proposes an dynamic flow classification method for IP Switching. By dynamically adjusting the values of its control parameters in response to the present usage of the hardware switching resources, this dynamic method can efficiently match the varying IP traffic and thus improve the performance of an IP switch.