  A valence QCD theory is developed to study the valence quark properties of
hadrons. To keep only the valence degrees of freedom, the pair creation through
the Z graphs is deleted in the connected insertions; whereas, the sea quarks
are eliminated in the disconnected insertions. This is achieved with a new
``valence QCD'' lagrangian where the action in the time direction is modified
so that the particle and antiparticle decouple. The theory has the vector and
axial $U(2N_F)$ symmetry in the particle-antiparticle space. Through lattice
simulation, it appears that this is dynamically broken down to $U_q(N_F) \times
U_{\bar{q}}(N_F)$. Furthermore, the lattice simulation reveals spin degeneracy
in the hadron masses and SU(6) relations in the ratios of $F_A/D_A, F_S/D_S$,
and $\mu^n/\mu^p$. This leads to an approximate $U_q(2N_F) \times
U_{\bar{q}}(2N_F)$ symmetry which is the basis for the valence quark model. We
find that the masses of N, $\Delta, \rho, \pi, a_1$, and $a_0$ all drop
precipitously compared to their counterparts in the quenched QCD calculation.
This is interpreted as due to the disapperance of the `constituent' quark mass
which is dynamically generated through tadpole diagrams. Form the near
degeneracy between N and $\Delta$ for the quark masses we have studied (ranging
from one to four times the strange mass), we conclude that the origin of the
hyper-fine splitting in the baryon is largely attibuted to the Goldstone boson
exchanges between the quarks. These are the consequences of lacking chiral
symmetry in valence QCD. We discuss its implication on the models of hadrons.
