  We have performed a study of the isovector, octet and singlet axial charges
of the proton in an extended chiral constituent quark model, where all the
possible $uudq\bar{q}$~($q=u,d,s$) five-quark Fock components in the proton
wave function are taken into account. The $^3P_0$ quark-antiquark creation
mechanism is assumed to account for the transition coupling between three- and
five-quark components in proton, and the corresponding transition coupling
strength is fixed by fitting the intrinsic sea flavor asymmetry
$\bar{d}-\bar{u}$ data for proton. Accordingly, with all the parameters fixed
by empirical values, the probabilities of the intrinsic five-quark Fock
components in proton wave function should be $\sim30 - 50\%$, which lead to the
numerical results for quark spin $\Delta u$, $\Delta d$ and $\Delta s$, as well
the axial charges of proton consistent with the experimental data and
predictions by other theoretical approaches.
