Abstract This paper presents the Fusion Virtual Assembly System FVAS 1.0 which makes possible engineering application for assemblies of large-scale complex nuclear facilities. This system focuses on utilizing a desktop virtual environment tightly coupled with commercial Computer Aided Design (CAD) systems, and is designed to support assembly planning, evaluation, demonstration, and training, and to work on personal computer (PC) platform. Main features of FVAS include: (1) automatic assembly modeling, (2) separation of display scene and collision detection scene, (3) multi-way assembly planning, (4) records and replays of assembly processes. This paper describes the system architecture, features and capabilities of FVAS. And tests conducted using real-world engineering models are also described.