A method and system for fusing image data. The method may include obtaining a first volume image and a second volume image. The method may further include casting a plurality of rays through at least one of the first volume image or the second volume image. Each of the plurality of rays may correspond to a pixel of an image to be displayed. For each of at least a portion of the plurality of rays, the at least one processor may further be directed to cause the system to set a series of sampling positions along the ray. The method may further include selecting a reference position from the series of sampling positions. The method may further include determining fusion data of the ray. The method may further include determining a pixel value of a pixel of the image to be displayed that corresponds to the ray.