This article provides an overview of Cloud Computing. It summarizes the definition of cloud computing，explores the characteristics of cloud computing，discusses the architecture and layer of cloud computing，It lists the major industry product in each layer. Through a running example of a building and hosting a website，this article pictures how to use cloud computing service，and reveals the benefits of cloud computing. This article also briefly covers the issues in cloud computing. This article addresses the potential of cloud computing in the context of Internet of Things，and anticipates the future of the usage of cloud computing in Internet of Things.