The invention relates to a connected domain marking method used for a projection interaction system, and solves the defect of low efficiency of the connected domain marking method in comparison with the method in the prior art. The connected domain marking method comprises the following steps that the connected domain of a first frame of image is marked, an image video is acquired, the connected domain of the first frame of image of the image video is marked and a marked graph corresponding to sub-rows is obtained; new pixels and disappear pixels are acquired; marking result correction is performed on the previous frame of image based on the disappear connected domain; and marking result correction is performed on the current frame of image based on the new connected domain. The marking function of the connected domain in the binary image can be rapidly completed in processing successive frames of images.