Abstract:China is the country with land earthquake taking place frequently. All the two big earthquakes during 20 century in the world,which caused more than 200 000 lives lost,took place in China. Land earthquake is mainly caused by fault activity and quick transmission of earthquake waves in land. Earthquake disaster is controlled by two main factors,site condition and base rock condition. The consideration of site condition is usually made in earthquake disaster prediction,but less attention is paid to base rock condition. As densely populated area with highly developed civilization,city shows obvious fragility to natural disasters. Tangshan,as a heavy industry city with six million populations,is located in the north east of Heibei province,China,and has been frequently suffered from natural disasters such as earthquake,karst collapse and ground collapse. The Big Earthquake in 1976 of Tangshan still remained freshly in people’s memory,which caused 240 000 lives lost,and especial attention has been paid to disaster resistance. Earthquake affecting coefficient is one of the most important factors for earthquake security evaluation,but it is very difficult to determine earthquake affecting coefficient accurately because of the influence of underground rock conditions. Traditional methods couldn’t analyse well earthquake resistance in city and engineering construction. Based on numerical calculating results of energy,and cracking probality in undeground base rock,the influences of these factors on earthquake affecting conefficient are analyzed. According to the base rock condition parameters,neural network method is applied,and the relation among earthquake affecting coefficient,energy,displacement and cracking probablity of undergroud rock is determined. The calculating model of earthquake affecting coefficient is constructed and the distribution of earthquake affecting coefficient in Tangshan city is calculated. From the calculating results,it is found that the earthquake affecting conefficient in southeast of Tangshan city is bigger than 0.48,even more than 0.64 somewhere,which means that the intensity of earthquake disaster is 10 degree. At last,some suggestions for city planning and engineering construction are given.