Abstract: The invention relates to a transdermal microneedle unit and a transdermal microneedle drug delivery device comprising the transdermal microneedle unit. The transdermal microneedle unit comprises a plurality of sheets stacked with each, each the sheet having at least one through hole defined thereon and a barbule arranged at the peripheral of the through hole, wherein the through hole on one sheet is penetrated by the barbules of other sheets and the barbules being juxtaposed to form at least one triangular pyramidal transdermal microneedle. The transdermal microneedle drug delivery device comprises a substrate, a transdermal microneedle unit, a union joint and an injection syringe.