The invention provides a method for measuring characteristic impedance of an electric transmission line. The method is suitable for measuring characteristic impedance of an electric transmission line via a first probe and a second probe. A first characteristic impedance where the first probe and the second probe are directly interconnected to each other is first measured. Then a second characteristic impedance where the first probe and the second probe are connected to the electric transmission line at the same time is measured from the first probe and the second probe. The characteristic impedance of the electric transmission line can then be obtained according to the first characteristic impedance and the second characteristic impedance.