  We calculate the angular scale of the acoustic oscillation from the BOOMERANG
and WMAP data on the cosmic microwave background (CMB) to constrain the
holographic dark energy model recently proposed by Li. We find that only the
phantom-like holographic dark energy survives the cosmological tests. This is,
however, inconsistent with the positive energy condition implicitly assumed in
constructing Li's model. Therefore the model is marginally ruled out by the
present CMB data. As a supplementary check, we also calculate the suppression
of the matter density fluctuation due to the late time integrated Sach-Wolfe
effect by the holographic dark energy, the result is within the tolerance of
the cosmic variance. Some aspect about the saturation of the cosmic holographic
bound is also discussed.
