The advantages of high access speed and differentiated service provisioning with WiMAX technology has made it competent with current wired networks solutions. The various service types have been defined in recent 802.16 standards. However, the detailed traffic scheduling algorithm has been left empty to researchers. In this paper, the new concept of urgency index (UI) is brought out as the system parameter to monitor different traffic services. UI is a set of system variables to reflect the urgency of bandwidth need for a specific service flow. Traffic scheduling is done based on the UI values. For different types of services, different UI changing profiles have been proposed to achieve best scheduling outcome. This scheme was implemented and simulation results have been compared to other proposed scheduling algorithms to evaluate its performance. The results show the UI based scheduling algorithm can achieve lower packets drop rate and also lower mean delay time at all traffic loads