<p>The earth tide can trigger earthquakes, and earthquakes can trigger large-scale landslides. This leads to the hypothesis that the earth tide might trigger large-scale landslides. The additional stress caused by the earth tide, named “tidal stress,” is derived in accordance with the theory of earth tide. The equation of tidal stress is a spatiotemporal function that is dependent on both the Julian day time and the location under the Equatorial coordinate system. The equation of the stability of large-scale landslides has been enhanced to incorporate tidal stress. Based on a number of instances of different failure modes of large-scale landslides, the variation of the factor of safety is approximately 8%, which substantiates the assertion that the earth tide has the capacity to precipitate the failure of large-scale landslides with a factor of safety approaching 1, such as slopes that have previously failed but are currently stable.</p>