Abstract: The paper focuses on obtaining a modified earthquake random model by introducing the structure affecting factor (T) into spectral density function with appropriate consideration of the structural effect on random process of ground motion.Besides,the key parameters in the model are studied in details and calculated by numerical method.The numerical results show that the structure affecting factor,determined by the equaling rules to code spectrum,is clear as a notion of physics and easy for application.In the mean time,the random mean spectrum of SDOF system derived from the modified model are well agreed with the code spectrum.The random model proposed in the paper is of relatively high accuracy and possess broad prospects of application,which will provide random seismic response analysis and dynamic reliable design with dependable references.