A method for image synthesis, a device for image synthesis and a storage medium. The method includes: performing a convex hull extraction on a target object image in an image to be processed to obtain a first boundary frame line; zooming out the first boundary frame line to obtain a second boundary frame line; determining, according to the target object image, at least one target ray where at least one connection point is located in synthesizing a first preset material with the target object image; determining the at least one connection point between the first preset material and the target object image; and synthesizing the first preset material and the target object image. The position of the first preset material in the synthesis result subjected to the image synthesis can be relatively reasonable, an image synthesis effect expected by a user can be achieved.