This study investigates the effect and permanency of a virtual reality (VR) based training method on complex assembly task performance and product quality. The correct assembly of a complex industrial product is crucial to reduce the production flaw in manufacturing. For this reason, a VR training set was developed for a hydraulically-controlled clutch complete set (HCCCS), consisting of 90 parts, to investigate the effectiveness and permanency of assembly training. A highly reliable measurement tool (KR-20 = 0.81) was developed to measure the participants' assembly task performance for this study. Two different experimental designs were used to firmly control threats to internal validity, such as testing, subject characteristics, maturation, and regression. One hundred and twelve factory workers who had no VR and assembly experience were assigned to the randomized post-test-only control group design (n = 56) and the randomized pre-test/post-test control group design using matched subjects (n = 56). In addition, training permanency was investigated, and the HCCCS quality reports were monitored every month for 6 months. The study results revealed that the VR-based training method reduced the training time per individual by 25% and achieved a 27.9% improvement in complex industrial assembly task performance. The quality reports also showed that the HCCCS assembly flaw rate was reduced by 89% and maintained the permanency of the VR-based training in complex industrial maintenance and assembly (IMA) tasks.