This paper evaluates 26 radon wells in Gansu province including their type of construction, the environment of their outcrop, the technique for observation, the instruments and equipments, the quality of data and the capacity of reflecting earthquakes, especially after the analysis of five moderate and strong earthquakes, proving the existence of radon message for earthquakes and the capacity of monitoring earthquakes by radon observation net, And then this paper also analyses the major reason why earthquakes can not be predicted effectively at present.