  Hadron and string cascade model (JPCIAE) with the hypothesis without
introducing the quark-gluon plasma (QGP), is employed to study the direct
photon and $\pi^0$ transverse momentum distributions for central
$^{208}$Pb+$^{208}$Pb collisions at 158A GeV/c . JPCIAE model, is based on LUND
model, especially on the envent generator PYTHIA, and can be used to simulate
the relativistic nucleus-nucleus collisions where PYTHIA is called to deal with
hadron-hadron collisions. In our work, the theoretical results of transverse
momentum distribution for both the direct photon and the $\pi^0$ particle are
lower than the data of WA98 experiment. However, JPCIAE model can ever explain
successfully the results of WA80 and WA93 experiments of central S+Au
collisions at 200A GeV/c where no evidence of direct photon excess. Having
considered the results of WA80 and WA93 experiments can be explained but WA98's
can't, that might provide a circumstantial evidence for the possible production
of QGP in the high-energy central Pb+Pb collisions.
