Abstract: A digital jitter synthesizer includes a signal generation unit, a tuning frequency optional unit, and a random option unit. The tuning frequency optional unit is able to output a frequency control value, and leads the signal generation unit tune the frequency of an output signal based on the frequency control value; then the signal with the frequency can be fed back to the random optional unit to lead the tuning frequency optional unit generate the other frequency control value randomly to control the signal generation unit for tuning the output signal to the other frequency then to generate an output signal with jitter effect.