To solve the problems of low efficiency, weak maintenance in development of task management system, model classes of task management system are abstracted and designed in this paper. The design and implementation of the model classes with versatility and applicability are introduced in detail. The model classes are applied in the existing task management system, which has been verified, improved, and optimized. The method of model classes will reduce cost of developing similar systems. It is also helpful to the research and implementation of task management system platform.