  The holographic $\Lambda(t)$CDM model in a non-flat universe is studied in
this paper. In this model, to keep the form of the stress-energy of the vacuum
required by general covariance, the holographic vacuum is enforced to exchange
energy with dark matter. It is demonstrated that for the holographic model the
best choice for the IR cutoff of the effective quantum field theory is the
event horizon size of the universe. We derive the evolution equations of the
holographic $\Lambda(t)$CDM model in a non-flat universe. We constrain the
model by using the current observational data, including the 557 Union2 type Ia
supernovae data, the cosmic microwave background anisotropy data from the 7-yr
WMAP, and the baryon acoustic oscillation data from the SDSS. Our fit results
show that the holographic $\Lambda(t)$CDM model tends to favor a spatially
closed universe (the best-fit value of $\Omega_{k0}$ is -0.042), and the 95%
confidence level range for the spatial curvature is $-0.101<\Omega_{k0}<0.040$.
We show that the interaction between the holographic vacuum and dark matter
induces an energy flow of which the direction is first from vacuum to dark
matter and then from dark matter to vacuum. Thus, the holographic
$\Lambda(t)$CDM model is just a time-varying vacuum energy scenario in which
the interaction between vacuum and dark matter changes sign during the
expansion of the universe.
