As a kind of adverse geological phenomenon developed in the Loess Plateau, hidden holes in loess have become one of the main causes of highway damage in loess areas of China. On the basis of a deep study on the development characteristics of hidden holes in loess, the collapse mechanism under earthquake was simulated by the finite element method. The dynamic responses of three types of high-slope loess subgrade (subgrade without hidden hole, subgrade with arched hidden hole, and subgrade with triangle hidden hole) under seismic load were obtained, and the ground motion amplification effect of hidden holes on the high-slope loess subgrade was analyzed. The results showed that the hidden holes in loess has the effect of ground motion amplification. With the same hole diameter and buried depth, the amplification effect of arched hidden holes on the peak horizontal acceleration of high-slope loess subgrade is more obvious than that of triangular hidden holes, especially on the slope shoulder and hole roof. It is suggested that due to the existence of hidden holes in loess, the high-slope loess subgrade is prone to collapse and destroy under earthquake.