Though not all active faults will generate strong earthquake, people still turn pale at only mention of them. Strong earthquake will take place only on a fraction of the active faults in a time scale as long as tens or hundreds of years, so we call them the macroseism generating fault. The macroseism generating fault is not merely a line but has a certain width from several meters to tens or hundreds of meters or more. During a strong earthquake, the seismic intensity may increase abruptly by 2 to 3 or more degrees along the fault, so it brings forth much difficulty to anti-seismic design, or nearly makes the design impossible. Off the fault, the seismic peak ground acceleration decreases with distance. In anti-seismic design, the commonly-used seismic ground motion parameters(or the seismic intensity)often have a bigger anti-seismic potential, e.g. a building with a design acceleration of 0. 15g(intensity Ⅶ°)may actually resist a damage of 0. 5g(Ⅸ°). The discovery of macroseism generating fault enables us to deal with the three factors, i.e. the time, location and magnitude, of earthquake prediction from another aspect. When using the"ground motion parameter zoning map" in urban planning, correction and amendment are necessary as for whether or not the macroseism generating fault exists and its influences.