  The phase space analysis of cosmological parameters $\Omega_{\phi}$ and
$\gamma_{\phi}$ is given. Based on this, the well-known quintessence cosmology
is studied with an exponential potential $V(\phi)=V_{0}\exp(-\lambda\phi)$.
Given observational data, the current state of universe could be pinpointed in
the phase diagrams, thus making the diagrams more informative. The scaling
solution of quintessence usually is not supposed to give the cosmic
accelerating expansion, but we prove it could educe the transient acceleration.
We also find that the differential equations of system used widely in study of
scalar field are incomplete, and then a numerical method is used to figure out
the range of application.
