  The observed acceleration of the present universe is shown to be well
explained by the holographic dark energy characterized by the total comoving
horizon of the universe ($\eta$HDE). It is of interest to notice that the very
large primordial part of the comoving horizon generated by the inflation of
early universe makes the $\eta$HDE behave like a cosmological constant. As a
consequence, both the fine-tuning problem and the coincidence problem can
reasonably be understood with the inflationary universe and holographical
principle. We present a systematic analysis and obtain a consistent
cosmological constraint on the $\eta$HDE model based on the recent cosmological
observations. It is found that the $\eta$HDE model gives the best-fit result
$\Omega_{m0}=0.270$ ($\Omega_{de0}=0.730$) and the minimal
$\chi^2_{min}=542.915$ which is compatible with $\chi^2_{\Lambda {\rm
CDM}}=542.919$ for the $\Lambda$CDM model.
