  We introduce a parton and hadron cascade model PACIAE 3.0 based on PYTHIA
6.428 and the PACIAE 2.2 program series. The simulation framework of C-, B-,
and A-loops are designed for the high energy ($\sqrt{s_{NN}}\geq 3$ GeV) and
low energy ($\sqrt{s_{NN}}<3$ GeV) nuclear collisions, respectively, in PACIAE
3.0. In the C-loop simulation, the parton-parton inelastic scattering processes
are added in the partonic rescattering process. The single string structure and
multiple string interaction mechanism have been introduced investigating the
strangeness enhancement in C- and B-loop. An improved mapping relation between
the centrality percentage definition and the impact parameter definition is
proposed responding the observation of $b_{max}\approx 20$ fm from ALICE,
ATLAS, and CMS collaborations. We have extensively modified the
phenomenological coalescence hadronization model. The PACIAE 3.0 model
simulated results of particle yield, transverse momentum distribution, and
rapidity distribution well reproduce, respectively, the experimental data
measured at FOPI, E895, RHIC, and LHC energies.
