  Based on the calculations using the lattice QCD by RBC-UKQCD collaboration
and a large $N_c$ dual QCD, the resulted $\epsilon'/\epsilon$, which is less
than the experimental data by more than a $2\sigma$ in the standard model (SM),
suggests the necessity of a new physics effect. In order to complement the
insufficient $\epsilon'/\epsilon$, we study the extension of the SM with a
colored scalar in a diquark model. In addition to the pure diquark box
diagrams, it is found that the box diagrams with one $W$-boson and one diquark,
ignored in the literature, play an important role in the $\Delta S=2$ process.
The mass difference between $K_L$ and $K_S$ in the diquark model is well below
the current data, whereas the Kaon indirect CP violation $\epsilon_K$ gives a
strict constraint on the new parameters. Three mechanisms are classified in the
study of $\epsilon'/\epsilon$, and they include: tree-level diagram, QCD and
electroweak penguins, and chromomagnetic dipole. Taking the Kobayashi-Maskawa
phase as the unique CP source, we analyze each contribution of the three
mechanisms in detail and conclude that these diquark-mediated effects can
singly enhance $\epsilon'/\epsilon$ to be of ${\cal O}(10^{-3})$, depending on
the values of free parameters, when the bound from $\epsilon_K$ is satisfied.
