Abstract
In this paper, we use the type Ia supernova data to constrain the model of holographic dark energy. For d = 1, the best fit result is Ωm0 = 0.25, the equation of the state of the holographic dark energy wΛ0 = −0.91 and the transition between the decelerating expansion and the accelerating expansion happened when the cosmological red-shift was zT = 0.72. If we set d as a free parameter, the best fit results are d = 0.21, Ωm0 = 0.46, wΛ0 = −2.67, which sounds like a phantom today, and the transition red-shift is zT = 0.28.