The invention provides a method for constructing a multi-level three-dimensional terrain model through multi-source data fusion. The method sequentially comprises the steps of image control point measurement and setting, unmanned aerial vehicle flight and data processing, three-dimensional laser scanning data acquisition and processing, terrain design and satellite terrain processing, multi-sourceimage data fusion, multi-source point cloud data fusion and multi-source DEM fusion. Finally, a three-dimensional terrain model is constructed, a single-source DOM + single-source DEM fusion mode, amulti-DOM + single-source DEM fusion mode and a multi-DOM + multi-DEM fusion mode are established, and a multi-level and multi-precision three-dimensional real terrain model is constructed. The problems that an existing three-dimensional terrain model is low in precision, single in obtaining mode, poor in expression effect, poor in construction guidance and the like are solved. The invention belongs to the field of constructional engineering.