  The simplest Higgs-portal scalar dark matter model, in which a real scalar
singlet is added to the standard model, has been revisited, by taking into
account the constraints from perturbativity, electroweak vacuum stability in
the early Universe, dark matter direct detection, and Higgs invisible decay at
the LHC. We show that the {\it resonant mass region} is totally excluded and
the {\it high mass region} is reduced to a narrow window $1.1$ ~TeV $\leq m_{s}
\leq$ $ 2.55$~ TeV, which is slightly reduced to $1.1$~TeV $\leq m_{s} \leq$ $
2.0$~ TeV if the perturbativity is further imposed. This {\it high mass range}
can be fully detected by the Xenon 1T experiment.
