  With only the tree level operator, the decay of $\Lambda_b\rightarrow pK$ is
predicted to be one order smaller than the experimental data. The QCD penguin
effects should be taken into account. In this paper, we explore the one-loop
QCD corrections to the decay of $\Lambda_b\to pK$ within the framework of QCD
factorization approach. For the baryon system, the diquark approximation is
adopted. The transition hadronic matrix elements between $\Lambda_b$ and $p$
are calculated in the light front quark model. The branching ratio of
$\Lambda_b\rightarrow pK$ is predicted to be about $4.85\times 10^{-6}$ which
is consistent with experimental data $(4.9\pm 0.9)\times 10^{-6}$. The CP
violation is about 5\% in theory.
