  The space and time evolution of initial parton production in
ultrarelativistic heavy ion collisions is investigated within the framework of
perturbative QCD which includes both initial and final state radiations.
Uncertainty principle is used to relate the life time of a radiating parton to
its virtuality and momentum. The interaction time of each hard or semihard
parton scattering is also taken into account. For central $Au+Au$ collisions at
$\sqrt{s}=200$ GeV, most of the partons are found to be produced within 0.5
fm/c after the total overlap of the two colliding nuclei. The local momentum
distribution is approximately isotropical at that time. The implication on how
to treat correctly the the secondary scattering in an ultimate parton cascading
model is also discussed.
