A method for detecting and separating vertical and horizontal synchronous signals from a computer system. The input forms of the vertical and horizontal synchronous signals from the computer system are detected by scanning a vertical synchronous signal terminal, a horizontal/composite synchronous signal terminal and a synchronous-on-green terminal of the computer system. In accordance with the detected input forms, the vertical and horizontal synchronous signals are separated from each other and then adjusted in polarity. Therefore, the present invention requires no separate hardware for the separation and polarity adjustment of the vertical and horizontal synchronous signals, resulting in simplification in circuit construction and reductions in number of used components and size of a printed circuit board.