The disclosure provides a voltage droop monitor (VDM) and a voltage droop monitoring method. The method includes: receiving a first reference clock signal and delaying the first reference clock signal as a first clock signal; delaying the first clock signal as a corresponding second clock signal; receiving the corresponding second clock signal from the corresponding first DCDL and generating a corresponding third clock signal via modifying a phase of the corresponding second clock signal; receiving the corresponding third clock signal; receiving a second reference clock signal; and collectively outputting a TDC code combination based on the second reference clock signal and the corresponding third clock signal, wherein the TDC code combination varies in response to a voltage variation of a to-be-monitored voltage.