The global communication puts a strong demand on the “one global network”. However, the public Internet faces great challenges to achieve this goal due to its inherent mechanisms. In this paper, we propose the global Overlay Cloud Network (OCN), a generic high-quality network built on the global public clouds, to accelerate global communications. We implement the OCN by three key techniques. First, we develop an automated topology planning technique to select the best candidate cloud nodes. Second, we design a novel time-varying routing technique to compute the best routes of OCN. Third, we implement a new dynamic transport layer to provide high-quality data transmission through OCN. We evaluate our prototype of OCN on real public cloud platforms. The results show that OCN substantially outperforms the existing underlay network with the RTT latency decreased by 15.2%, the packet loss rate reduced by 1.9% and throughput improved by 10X.