Abstract: According to preventative maintenance scheduling for Multi-products and Semi-flexible Parallel Production Line (MSPPL) in semiconductor chipset assembly and test factories, the preventive maintenance scheduling model for MSPPL is proposed with the maximal production time as the objective function and under four constraints semi-flexible limits, multi-product production time requirements, preventive maintenance time windows, and the amount of preventive maintenance worker group. The proposed model has been applied in the multi-products and semi-flexible parallel production line of a chipset assembly and test factory by using the software named lingo (version is 9.0). The scheduling results have been successfully applied the actual production, which validates the feasibility and accuracy of the proposed model.