The multiplicity and ?/ ratio are studied by hadron transportation string fragmentation model in relativistic heavy ion collisions. Firstly, the dependence of multiplicity and ?/ ratio on the system size and the collision centrality is studied. It shows that the and multiplicities go up as the increase of system size and the increase of collision centrality. However, their ratio keeps almost a constant. The effect of annihilation cross section to multiplicity and ?/ ratio is also studied. It is found that this effect is weak: multiplicity and ?/ ratio have a little amount of increase by the decrease of annihilation cross section. Even the cross section is down to zero, ?/ ratio is only 1.2 in 200 A GeV AuAu head on collision. The ?/ ratio is obtained to be 0.28 in pp collision, lying in the range of experimental data:0.2—0.3. It is also obtained that the ratio in AA collisions is 3—5 times of that in pp collision.