A P2P (peer-to-peer) network based large-scale live video streaming system called Gridmedia is presented in this paper. In this system, a gossip-based protocol is adopted to construct an unstructured application layer overlay. Each peer independently selects its own neighbors and uses a push-pull streaming method to fetch data from neighbors. Compared with the pure pull method of DONet, push-pull method greatly diminishes the accumulated latency observed at end users and efficiently reduces the control overhead of streaming system, both of which are evaluated by the experiments on PlanetLab. A prototype system of Gridmedia has been developed to broadcast the Spring Festival Gala Evening in 2005 over global Internet with 300Kbps video stream and attracted more than 500 000 users all over the world with the peak concurrent online users of 15 239 during the event.