In order to automatically measure a signal skew between a first test signal and a second test signal by using an oscilloscope, a method is provided by the present invention. The method includes: capturing a band center of the first test signal; capturing a first sampling point and a second sampling point of the second test signal; comparing a voltage difference between the first sampling point and the second sampling point of the second test signal with a threshold value so as to decide and capture a rising band center and a falling band center of the second test signal. By using the invented method, the signal skew between the first test signal and the second test signal can be calculated according to the band center of the first test signal, the rising band center and the falling band center of the second test signal.