We are the electronics assembly company in China. Recently, we implement the ISO14000 for our company zone. Since the closing areas include several factories, dormities, canteens, the environmental improvement expense will probably be more than 1 million dollars. We would like to know some feasible ways we could to certify our company for factories only. It is expected to save about 0.7 million dollars if exclusive of dormities and canteens. Now, the question is, is it the acceptable method to set up steel-wire-chain / wall to partition such areas?

You don't need to build a wall (unless you want to). Have your registration note that it covers your "factories". Don't even mention your dorms & canteens.
The ISO-14001 registration covers your management system. This system needs to have effective ways for ensuring you comply with laws, take steps to prevent pollution & show continual improvement. If you are committed to doing this in your factories you should be OK.