The invention provides a dither measuring device and method thereof. The dither measuring device comprises a signal picking module, a signal amplification module, an edge detection module and a time-to-digital conversion module. The signal picking module receives the signal to be measured, and outputs a first impulse signal whose pulse width is same as the period width of the signal to be measured; the signal amplification module amplifies the pulse width of the first impulse signal to generate a second impulse signal; the edge detection module generates a first indicator signal and a second indicator signal according to the rising edge and the failing edge of the second impulse signal respectively; the time-to-digital conversion module converts the pulse width of the second pulse signal on time domain into digital signal according to the first and second indicator signal to gain the dither valve of the signal to be measured.