The duration of earthquake ground motion is acted as one of the three elements indicating of ground motion. Its influence on earthquake damage is gradually recognized by experts and scholars all over the world. However, in defining of duration, there is currently no uniform and clear concept. In a generalized definition, the paper gives the definition about the total duration of earthquake ground motion and the duration of strong ground motion. The researchers select more suitable duration according to the characteristics of their respective fields. The duration can be roughly divided into two broad categories: absolute duration and relative duration. The absolute duration is bracket duration based on absolute acceleration threshold, while the relative duration of energy control reflects the trend of intensity or energy change in the seismic process. There are many definitions of the duration, yet this paper simply reviews five definitions of duration of earthquake ground motion. The characteristics of the five kinds of duration definitions are analyzed meticulously. Moreover, the paper introduces the research results in prediction model of duration of earthquake ground motion. At last, the paper puts forward some insights of current application in duration of earthquake ground motion.