Abstract: In order to reduce the uncertainty introduced from the transformation of base rock response spectrum into natural or artificial earthquake wave, a method of calculating ground acceleration response spectrum directly according to base rock response spectrum is presented. This method is base on the presumption that the input is a Gaussian stationary random process. In the course of finding solution, the effect of soil non-linearity is taken into account in the light of the principle that the shear strain is subject to uniform distribution, at the same time, the effect of base rock radiation damping is incorporated as well. Examples show that the calculation work of this method needs less computation effort than other methods, with reliable precisions.