Abstract: Horizontal earthquake force is traditionally regarded as a decisive part in destruction of engineering structures during earthquakes. Having analyzed a wide variety of damages to many kinds of structures, we come to the conclusion that it is the vertical earthquake force which plays the decisive role in the destruction of structures during earthquakes. Through investigation of earthquake damages in China, this fact can be directly perceptible. In recent years, many authors of various countries, have also noticed this question so that the effects of the vertical force in their respective building codes are greatly increased. Therefore, the problem on the magnitudes of the vertical earthquake force has come to be widely discussed among earthquake engineering circles.Now the problem of computational technique in structural analysis using accelerograms has been generally solved. However, the real damping and the mechanical behavior of the structures during earthquakes, especially the complicated effect of the foundation are far from being clarified. So, it is impossible to estimate the reliability of the analysis.In this paper, phenomena of various ground objects during earthquakes have been studied. The vertical earthquake force on those objects are found to be much greater than those from traditional views. Explanations of various structural damages based on this new view are quite satisfactory. Therefore, a method of inversion for calculating certain parameters of the vertical earthquake force is here suggested.