Abstract: This paper investigates the layout design and optimization for an assembly line system in an industrial case based on the discrete event simulation (DES) technique. The purpose of the simulation system was to build up different layouts of the prepared manufacture system, to propose a solution designed to decrease the need for workforce and to settle bottlenecks problem in the system. In this study, based on the analysis of the manufacturing process of the typical manufacturing part and the available facilities in the assembly system, three layout designs are proposed based on straight-line, U-shape and parallel U-shape patterns respectively. A DES simulation environment by using the software of Witness is established in line with the machinery data provide by the company as well as the experiential data identified from the literature. The three layout designs are then tested in the simulation environment, whose simulation performances are compared and analyzed in terms of the line balance and production efficiency. The results show that the parallel U-shape line gives rise to the best solution.