The pseudorapidity distributions of charged particles produced in Cu-Cu collisions over an energy range from 22.4 GeV to 200 GeV are investigated by using a multi-source ideal gas model which contains systematically the contributions of leading nucleons. It is shown that the calculated results are in agreement with the experimental data and the model is successful in the description of the pseudorapidity distribution of charged particles. The contributions of leading nucleons increase with the increasing impact parameter. The cylinder length (the longitudinal shift of the interacting system) in rapidity space increases with the increasing energy and does not depend on centrality at a given energy.