Cost reduction is an important issue in the intense competition automotive industry. Interior parts which are mainly consist of plastic have same issue. The manufacturing main processes of plastic products are injection and assemble and the cost of injection depends on injection cycle time. Therefore many studies for the reduction of injection cycle time have been implemented. However the researches based on engineer's experiences have limits so, nowadays many studies utilize CAE. In this paper, the study for the reduction of cycle time focused on injection molding design. To satisfy appearance quality with the reduction of cycle time, the design of injection molding was optimized by using CAE. The result of CAE showed many causes and effects of problems. The optimization of injection molding design improved the quality with the reduction of cycle time. Finally, the product based on CAE showed good quality and cycle time reduction in comparison with previous products.