Recently, the Storage Networking Industry Association (SNIA) has released the first standard for cloud interoperability. With more and more standards for interoperability emerging, it can be expected that a global cloud resource exchange market will form. In such a market, it is challenging to present a dynamic pricing scheme to meet different requirements. To cope with the challenge, in this paper we first present a framework for constructing global cloud resource markets and then propose a knowledge-based continuous double auction (CDA) model that determines the price of cloud resources using a learning algorithm based on historical trading information. Experimental result shows that our model can attain high market efficiency as well as stable trading price.