  CP violation in the CKM mixing is discussed for the case of quark mass
degeneracy that is approximate in the quark mass hierarchy limit. Differing
from the traditional understanding of CP vanishing for degenerate masses, we
find degenerate symmetry plays a non-trivial role in CP violation. The minimal
flavor structure model is reviewed to demonstrate the role of degenerate
symmetry in quark flavor mixing, particularly in CP violation. This relation
between mass hierarchy and CP violation helps us understand the origin of CP
violation and assists the construction of the flavor model.
