Virtual reality (VR), as a new technology, is integrated with software systems for engineering, design, and manufacturing. The integration has given a new impetus to the field of computer-aided engineering. This paper presents a research effort aimed at creating a virtual plastic injection molding (VPIM) environment, which is designed and implemented based on techniques such as VR, multidiscipline simulation, and scientific visualization. The VPIM system includes two parts: designing in VPIM and evaluation in VPIM. It is the first system to scrutinize virtual prototype mock-ups of new products, machines and production processes in interactive graphic simulation. During the evaluating phase, coupled to appropriate computer-based reasoning and decision-support tools and driven by data from the real manufacturing environment, a realistic impression of the process of plastic injection molding and manufacture can be achieved and can be changed interactively, and it is possible to thoroughly examine the planned system and eventually detect and remove any defects and inadequacies. The construction approach and key techniques (FEA, virtual assembly, stereoscopic display, a triangulated boundary-representation of an approximating polyhedron, collision detection, etc.) of the system are described in detail. The overall system is a powerful new approach for highly relevant industrial application of VPIM which focuses on the construction and assessment of alternate manufacturing sequences and mold design in an early design stage. Improvement of the design and manufacturing process will lead to better design and reduced development time and cost.