  The thermodynamical properties of dark energy are usually investigated with
the equation of state $\omega =\omega_{0}+\omega_{1}z$. Recent observations
show that our universe is accelerating, and the apparent horizon and the event
horizon vary with redshift $z$. When definitions of the temperature and entropy
of a black hole are used to the two horizons of the universe, we examine the
thermodynamical properties of the universe which is enveloped by the apparent
horizon and the event horizon respectively. We show that the first and the
second laws of thermodynamics inside the apparent horizon in any redshift are
satisfied, while they are broken down inside the event horizon in some
redshift. Therefore, the apparent horizon for the universe may be the boundary
of thermodynamical equilibrium for the universe like the event horizon for a
black hole.
