The invention discloses a deformation monitoring method realizing timely alarm for a danger area, which relates to the field of deformation monitoring of dams, slopes, bridges, railways, highways and hillsides. The method includes the following steps: S1, installing equipment; S2, marking corner reflectors; S3, obtaining foundation SAR deformation information and laser scanner DEM information; S4, extracting the coordinates of the corner reflectors from the foundation SAR deformation information and DEM information; S5, unifying the coordinate systems of foundation SARs and 3D laser scanners; and S6, fusing a foundation SAR deformation displacement diagram and a 3D laser scanner DEM diagram. The invention aims to overcome the problem that it is difficult to predict the disaster in a danger area through the existing deformation monitoring method, and provides a deformation monitoring method realizing timely alarm for a danger area. Through the deformation monitoring method of the invention, the actual positions corresponding to largely deformed points in the foundation SAR displacement diagram can be acquired quickly and accurately, and the disaster in a danger area can be predicted in time.