  In this paper, we calculate the branching ratios of \Lambda_{b} \to pK^{-}
and p\pi^{-} decays in the flavor changing Z^{\prime} model. We find that the
branching ratios for these two decay modes are sensitive to the contributions
of Z^{\prime} boson. For \Lambda_{b}\to p K^{-} decay, if the left-handed
couplings are equal to the right-handed couplings, the branching ratio of this
decay could match up to the currently experimental data for \xi_{s}=0.01 and
-52^{\circ}<\phi^{L}_{s}<132^{\circ}, or \xi_{s}=0.004 and
0^{\circ}<\phi^{L}_{s}<84^{\circ}; if only the left-handed couplings are
considered, it could match up to the experimental data for \xi_{s}=0.01 and
-10^{\circ}<\phi^{L}_{s}<138^{\circ}$. And for \Lambda_{b} \to p\pi^{-} decay,
if the left-handed and right-handed couplings are equal, the branching ratio of
\Lambda_{b} \to p\pi^{-} decay may be consistent with the currently
experimental data with \xi_{d}=0.05 and -135^{\circ}<\phi^{L}_{d}<43^{\circ},
if only the left-handed couplings are considered, it may be consistent with
\xi_{d}=0.05 and -114^{\circ}<\phi^{L}_{d}<8^{\circ}.
