  Recent observations confirm that our universe is flat and consists of a dark
energy component $\Omega_{DE}\simeq 0.7$. This dark energy is responsible for
the cosmic acceleration as well as determines the feature of future evolution
of the universe. In this paper, we discuss the dark energy of universe in the
framework of scalar-tensor cosmology. It is shown that the dark energy is the
main part of the energy density of the gravitational scalar field and the
future universe will expand as $a(t)\sim t^{1.3}$.
