In a new optical hybrid switching environment which combined Optical Burst Switching (OBS) and Optical Circuit Switching (OCS), we propose flow-level service classification scheme for IP differentiated service. In particular, this classification scheme classifies incoming IP traffic flows into short-lived and long-lived flows for Quality of Service (QoS) provisioning according to traffic characteristics such as flow bandwidth, loss and delay. In this hybrid switching, the short-lived flows including delay sensitive traffic use OBS and the long-lived flows including loss-sensitive traffic use OCS. Therefore, optical hybrid switching network can take advantages of both switching technologies using the proposed flow classification scheme. The aim of proposed technique is to maximize network utilization while satisfying user's QoS requirements.