ShakeAlert earthquake early warning system in the west coast of the United States can issue alerts to the public before destructive seismic waves arrive, mitigating the hazards of earthquakes. After more than ten years of development, the research of ShakeAlert has been basically completed. On October 17, 2019, California began testing the ShakeAlert system version 2.0, and officially released earthquake early warning information to the state. This paper reviews the development of ShakeAlert, and introduces sensor networks, field telemetry, central processing architecture, testing and certification platform, alert distribution and end-user display in detail. The purpose is to analyze the great utility of the ShakeAlert 2.0 system in earthquake prevention and disaster mitigation and its reference to the development of Chinese earthquake early warning system.