In facility agriculture, it is an urgent problem to design and choose the type and facility of greenhouse based on user's requirements, which are always difficult to express clearly and definitely. An agent-based intelligence decision support system for designing virtual greenhouse is presented in this paper, in which one agent can reason the appropriate greenhouse skeleton type for users, while the agent of analyzing light distribution can sense the light ray and calculate the total solar energy inside greenhouse in a given day. 3D scene of the generated virtual greenhouse can be rendered in real time; users can edit the greenhouse model and walk through the scene interactively. The results demonstrate the proposed system may provide a new approach for computer-aided design of greenhouse.