To provide a landslide monitoring method and a system for highly accurately predicting the occurrence of a landslide.

Only pore water pressure is set as a variable, and a residual variable is periodically reviewed when planning a landslide preventive facility or thereafter. A safety factor by a stable analysis of a slope calculated as a renewing constant is set as a control safety factor, and the occurrence of the landslide of an object slope is monitored and predicted by the control safety factor obtained by substituting output from a pore water pressure measuring means 1 arranged in a landslide monitoring area.