We study the effects of the fourth quark generation model in Bs→π^-K^＋ decay. Combining with the up-to-date experimental measurement for B（Bs→π^-K^＋） dir - and Acp ^dir（Bs→π^-K^＋） by the CDF Collaboration, we derive the new bound of weak phase Фbd, which are 0° 〈 Фbd 〈 44°,321° 〈 Фbd 〈 360° and 0° 〈 Фbd 〈 26°, 342° 〈Фbd 〈 360° for mr, ： 400 and 600 GeV respectively. In these regions, B（Bs→π^-K^＋） and Acp^dir （Bs→π^-K^＋） consist with the current experimental data within errors.
In this paper, we calculate the branching ratios of Ab→pK^- and pπ^- decays in the flavor changing Z＇ model. We find that the branching ratios for these two decay modes are sensitive to the contributions of the Z＇ boson. For Ab→pK^- 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 ξs =0.01 and -52°〈 Ф^Ls 〈 132°, or ξs=0.004 and 0°〈Ф^Ls 〈84°; if only the left-handed couplings are considered, it could match up to the experimental data for ξs =0.01 and - 10° 〈 Ф^Ls 〈 138°. And for Ab→pπ^- decay, if the left-handed and right-handed couplings are equal, the branching ratio of Ab→pπ^- decay may be consistent with the currently experimental data with ξd =0.05 and -135°〈 Ф^Ld 〈43°, if only the left-handed couplings are considered, it may be consistent with ξd=0.05 and -114° 〈Ф^Ld 〈8°.
