A method, an image processing device, and a system for generating a depth map are proposed. The method includes the following steps. A first original image and a second original image are obtained, and first edge blocks corresponding to the first original image and second edge blocks corresponding to the second original image are obtained. Depth information of edge blocks is generated according to the first edge blocks and the second edge blocks, and depth information of non-edge blocks is set according to the depth information of the edge blocks. The depth map is generated by using the depth information of the edge blocks and the depth information of the non-edge blocks.