1. A method for detecting a salient region of a stereoscopic image, which is based on parallax effect and spatial dissimilarity, comprising the following steps: step 1) calculating flow information of each pixel by utilizing Sift Flow algorithm separately with respect to a left-eye view and a right-eye view of the stereoscopic image; step 2) matching the flow information of the left-eye view and the right-eye view, to obtain position displacements between corresponding pixel points in the two views as parallax values, thereby to obtain a parallax map; step 3) selecting one of the left-eye view and the right-eye view, dividing it into T non-overlapping square image blocks, each of the image blocks containing K 2 pixels; step 4) dividing the parallax map into image blocks corresponding to the image blocks divided in the step 3), calculating a parallax effect value for each of the image blocks of the parallax map; step 5) for each of the image blocks of the selected one of the left-eye view and the right-eye view, calculating a central bias feature value and a spatial dissimilarity value, and multiplying three values of the central bias feature value, the spatial dissimilarity value and the parallax effect value in the step 4), to obtain a saliency value of the image block; and step 6) replacing a saliency value of each pixel of each of the image blocks with the saliency value of the image block, normalizing saliency values of all of the pixels, to obtain a saliency gray scale map of the stereoscopic image.