The subgrade stability monitoring plays a significant role in subgrade construction quality control,whether determining effectively the stability of the subgrade is the focus and aporia. However,only a uniform threshold is presented for the determination of the subgrade stability in the current specification,there is no specific instructions for all kinds of subgrade,it has certain defects. In this paper,utilizing acceleration methods,by analyzing the positive and negative characteristic of the subgrade lateral horizontal displacement acceleration and the subgrade settlement center acceleration reflect the subgrade stability,and further showing the red sandstone subgrade stability decision threshold though combining the specification limits with construction experience,the threshold has a better guiding function in some similar subgrade filling construction quality control.