In order to meet the demand for deformation monitoring of rockfill dams of 200 m to 300 m, and to compensate for the deficiencies of using single-track synthetic aperture radar (SAR) data that can only measure two-dimensional deformation in the line of sight and azimuth directions, interferometric synthetic aperture radar (InSAR) measurements and conventional point monitoring data were fused across scales based on ensemble Kalman filtering to improve the monitoring accuracy of rockfill dam exterior deformation and multi-dimensional monitoring data were used to reconstruct exterior deformation field. Shuibuya concrete-face rockfill dam was taken as an example, and results show that the new monitoring technology with characteristic of “large range, low accuracy and high efficiency” and the conventional monitoring technology with characteristic of “discrete points, high accuracy and low efficiency” can complement each other through multi-source data fusion. By reconstructing the exterior deformation field based on multi-dimensional monitoring data, the overall deformation state of the rockfill dam can be comprehensively grasped and the possibility of missing or misjudging the actual deformation by using single-dimensional monitoring results can be reduced. The method can also be used for deformation monitoring and exterior deformation field reconstruction of the reservoir bank slopes.