Abstract: Grand canonical Monte Carlo (GCMC) method is adopted to investigate the dependence of hydrogen storage capacity on the diameter of a single-walled carbon nanotube (SWCNT), the distance between walls and the shell number of a multi-walled carbon nanotube (MWCNT),as well as the inter-tube distance and configuration of SWCNT array (SWCNTA),at 298K and 10MPa.The calculated results show that when the diameter of SWCNT approaches 6 nm the average number density (n_AV) of hydrogen within the tube reaches its maximum.When the difference between the internal radius and the external radius increases from 0.34 to 0.61 or 0.88 nm the hydrogen storage capacity is improved effectively.As the inter-tube distance of SWCNTA approaches 1.7 nm n_AV within the interstitial space of SWCNTA reaches its maximum and a square array is better than a triangular array for hydrogen physisorption.It is also found that n_AV within the interstitial space is larger than that within the tube whether for a square array or a triangular array,only if inter-tube distance is larger than 0.6 nm.The hydrogen storage capacity could be effciently increased by the reasonable choice of the diameter of SWCNT,the distance between walls of MWCNT,the inter-tube distance and configuration of SWCNTA.Conclusions are discussed and explained.