We investigate the observational signatures of the holographic dark energy model in this paper, including both the original model and a model with an interaction term between the dark energy and dark matter. We first delineate the dynamical behavior of such models, especially whether they would have a "Big Rip" for different parameters, then we use several recent observational data to give more reliable and tighter constraints on the models. The results favor the equation of state of dark energy crossing -1, and the universe ends in the "Big Rip" phase. By using the Bayesian evidence as a model selection criterion to make the model comparison, we find that the holographic dark energy models are mildly favored by the observations compared with the $% \mathrm{\Lambda CDM}$ model. ; Comment: Proceedings of the 8th UCLA Symposium: Sources and Detection of Dark Matter and Dark Energy in the Universe.Marina de Rey, Los Angles 20-22,Feb,2008.