Manufacturing system is a typical complex system, while task assignment problem is an important topic in manufacturing system. It is one of the most difficult problems in the theory research for manufacturing system. In this paper, task assignment model in manufacturing system was modeled with the concept of Holonic Manufacturing System including basic system model, communication model, represent model and optimization model. Task assignment model based on operation cost and lead time is applied to cooperative activity among orders in a Holonic community. A hybrid PSO algorithm was utilized to the combination of the task assignment problem. Simulation result shows that the model and the algorithm are effective to the problem.