An on-screen display system is located externally a KVM switch. The on-screen display system includes a first end, an on-screen display circuit, a switch circuit and a second end. The first end receives a video signal from a computer. The on-screen display circuit generates an on-screen display menu signal. The switch circuit receives the video signal from the computer and the on-screen display menu signal from the on-screen display circuit. The on-screen display system combines the video signal and the on-screen display menu signal, or overlaps the on-screen display menu signal on the video signal to be displayed on the display according to a control signal.