Abstract: Earthquake affecting coefficient is one of the most important factors for city seismic microzonation and engineering earthquake security evaluation. Because of the influence of underground rock conditions, it is very difficulty to determine earthquake affecting field precisely, the result, which come from traditional method,couldn’t meet the demand of earthquake resistant design in city and engineering construction.Therefore,the analysis of influence of base rock condition on earthquake affecting coefficient is necessary for earthquake security evaluation. By numerical simulation of underground rock fracture, the distribution of underground rock energy and fracture is calculated. Furthermore, neural network method is applied, and the calculating model of earthquake affecting coefficient is established based on the distribution of base rock fracture and energy. As an example, the calculated result of earthquake affecting field is analyzed and some suggestions for city planning and engineering construction are given.