Abstract: A measuring method for signal jitter comprises the following procedures: First, a first data signal is provided, and the first data signal is deemed equivalent to a second data signal, wherein frequency of the first data signal is a multiple (preferably odd) of that of the second data signal, and at the same time, the ascent and the descent edges of the second data signal are the same as that of the first data signal. The widths of the high and low levels of the second data signal are counted so as to generate an estimated jitter stream including the estimated jitter values of the ascent and the descent edges of the second data signal. Then, jitter distribution diagrams of the ascent and the descent edges are established based on the estimated jitter stream, so as to calculate an eye open (EO) value.