  A cosmology of Poincare gauge theory is developed, where several properties
of universe corresponding to the cosmological equations with the pseudoscalar
torsion function are investigated. The cosmological constant is found to be the
intrinsic torsion and curvature of the vacuum universe and is derived from the
theory naturally rather than added artificially, i.e. the dark energy
originates from geometry and includes the cosmological constant but differs
from it. The cosmological constant puzzle, the coincidence and fine tuning
problem are relieved naturally at the same time. By solving the cosmological
equations, the analytic cosmological solution is obtained and can be compared
with the LCDM model. In addition, the expressions of density parameters of the
matter and the geometric dark energy are derived, and it is shown that the
evolution of state equations for the geometric dark energy agrees with the
current observational data. At last, the full equations of linear cosmological
perturbations and the solutions are obtained.
