Using a hadron and string cascade model, JPCIAE, the experimental data of charged particle pseudorapidity density at mid-rapidity in both the relativisticp+p¯collisions and theAu+Aucollisions atsnn=130 GeVwere reproduced fairly well without retuning the model parameters. The predictions for full RHIC energyAu+Aucollisions and forPb+Pbcollisions at the LHC energy were given. Participant nucleon distributions were calculated based on different methods. It was found that the number of participant nucleons,⟨Npart⟩,is not a well defined variable both experimentally and theoretically. Thus, it is inappropriate to use charged particle pseudorapidity density per participant pair as a function of⟨Npart⟩for distinguishing various theoretical models. ©2001 American Institute of Physics.