  Coupling constants of the pseudoscalar mesons to the octet baryons are
calculated in the QCD sum rule approach. Two-point correlation function of the
baryons are evaluated in a single meson state and the vacuum, which yields the
designated coupling. The emphasis is on the flavor SU(3) structure of the
coupling constants and reliability in extracting the coupling constants from
the two-point correlation functions. We first calculate the baryon-diagonal
couplings and study the reliability of the sum rule. The F/D ratio of the
coupling is determined in the SU(3) limit. We further formulate the
baryon-off-diagonal couplings using the projected correlation functions and the
vertex functions, so that the unwanted excited states do not contaminate the
sum rule. As an example, the (\pi - \Lambda - \Sigma) coupling constant is
calculated and the flavor SU(3) breaking effect is studied. We find that the
effect of SU(3) breaking on the (\pi - \Lambda - \Sigma) coupling constant is
small.
