  We present in detail a four-dimensional unified quantum theory. In this
theory, we identify three class of parameters, coordinate-momentum, spin and
gauge, as all and as the only fundamental parameters to describe quantum
fields. The coordinate-momentum is formulated by the general relativity in
four-dimensional space-time. This theory satisfies the general covariance
condition and the general covariance derivative operator is given. In an
unified and combined description, the matter fields, gravity field and gauge
fields satisfy Dirac equation, Einstein equation and Yang-Mills equation in
operator form. In the framework of our theory, we mainly realize the following
aims: (1) The gravity field is described by a quantum theory, the graviton is
massless, it is spin-2; (2) The mass problem of gauge theory is solved. Mass
arises naturally from the gauge space and thus Higgs mechanism is not
necessary; (3) Color confinement of quarks is explained; (4) Parity violation
for weak interactions is obtained; (5) Gravity will cause CPT violation; (6) A
dark energy solution of quantum theory is presented. It corresponds to
Einstein's cosmological constant. We propose that the candidate for dark energy
should be gluon which is one of the elementary particles.
