Abstract: Two samples of silver sheet were analyzed by low energy ISS method. The sample 1 was earthed and sample 2 was floated during ISS analysis. It has been observed that serious charging effect occurred which caused the ion beam to be deflected for the electrically insulated sample 2, and the charging effect could be eliminated by using electron flood gun. Besides, it has been found that usage of electron flood gun did not increase the neutralization of inert gas ions.