User task is one of the major task types of complicated workflow applications. The way how to handle user tasks impacts the performance of a workflow system significantly, which involves many issues such as description of the duty of each participant, calculation of the workload of each participant, and policy to dispatch work items among participants. After analyzing the characteristics of user tasks, this paper proposes an efficient user task handling mechanism based on dynamic load-balance approach. To do this, the organization model and the workload model are defined, the load-balance policies and the workload dispatching algorithms are designed, and the implementing techniques in a prototype WfMS — e_ScopeWork are presented. The performance experiments are made and show that the new mechanism can improve the workflow system performance effectively.