Abstract: A depth calculating method is provided for calculating corresponding depth data in response to frame data, which includes macroblocks. The depth calculating method includes the following steps. First, a type of video is decided according to a video content. A motion vector is obtained from decompressed video information and is modified according to a shot change detection and camera motion data. Then, multiple pieces of macroblock motion parallax data respectively corresponding to the macroblocks are found according to motion vector data of the modified macroblocks. Thereafter, the depth data corresponding to the frame data is calculated according to the pieces of macroblock motion parallax data, variance data, contrast data and texture gradient data.