An apparatus for adaptive de-interlace of a frame comprises a line-segment difference-value calculating module, a motion-vector calculating module, an intra-block calculating module, a trigger-value producing module, and an image processing module. The line-segment difference-value calculating module computes a difference value of a line segment within the frame. The motion-vector calculating module computes a motion vector of a macro block that is located in the frame and comprises the line segment. The intra-block calculating module computes the amount of intra blocks in the frame. The trigger-value producing module determines whether the amount of the intra blocks is larger than a first threshold or not, so as to select an algorithm for generating a trigger value. The image processing module determines whether the trigger value is larger than a second threshold or not and then selects a de-interlace algorithm for de-interlacing the line segment.