A depth fusion method adapted for a 2D-to-3D conversion image processing apparatus is provided. The depth fusion method includes the following steps. Respective motion-based depths of a plurality of blocks in an image frame are obtained. An original image-based depth of each of the blocks is obtained. The original image-based depth of each of the blocks is converted to obtain a converted image-based depth of each of the blocks. The motion-based depth and the converted image-based depth of each of the blocks are fused block by block to obtain a fusion depth of each of the blocks. Furthermore, a depth fusion apparatus is also provided.