Effective distance to reduce seismic intensity on two sides of the main fault causing the 1920 Haiyuan M8.5 earthquake is about 160 km.Within the distance no M>6.5 earthquake will occur during the future several hundreds of years.Because Lanzhou City is 120 km away from the main fault, in the city no M>6.5 earthquake will occur in a few hundreds of years.Structures and buildings in Lanzhou City were designed according to antiseismic standard of Ⅷ degree on the intensity scale.Even though a M6.5 earthquake will occur in future,its destruction would not be too heavy.It is a consideration in the worst case.