  In $\XQM$, a quark can emit Goldstone bosons. The flavor symmetry breaking in
the Goldstone boson emission process is used to intepret the nucleon
flavor-spin structure. In this paper, we study the inner structure of
constituent quarks implied in $\XQM$ caused by the Goldstone boson emission
process in nucleon. From a simplified model Hamiltonian derived from $\XQM$,
the intrinsic wave functions of constituent quarks are determined. Then the
obtained transition probabilities of the emission of Goldstone boson from a
quark can give a reasonable interpretation to the flavor symmetry breaking in
nucleon flavor-spin structure.
