The embodiment of the present specification discloses an image synthesis method, apparatus and device for free-viewpoint. The method includes: correcting a first depth map based on a first color map and the first depth map inputted, wherein the first color map includes a left image and a right image, and the first depth map includes a left image and a right image; forward-projecting the second depth map to a virtual viewpoint position based on the pose of a virtual viewpoint to obtain a third depth map, where the third depth map is a projection map located at the virtual viewpoint position; back-projecting the left and right color maps closest to the virtual viewpoint position in the first color map to the virtual viewpoint position based on the third depth map to obtain a second color map, where the second color map is a projection view of the first color map at the virtual viewpoint position; correcting the second color map by using an optical flow algorithm to obtain a third color map, where the optical flow algorithm implements aligning the left and right images of the second color map; performing weighting calculation and blendering on the third color map to obtain a composite image.