In this paper, we report the experimental results of a two-pass amplification atomic iodine laser amplifier. For an iodine amplifier working under the condition lower than those in the saturation region, two-pass amplification can increase the efficiency of the iodine laser amplifier obviously.Besides,we found that He is the best among He, Ar, SF6 usually used as buffer gases in iodine lasers. It has obvious advantages especially in reducing the beam deformation produced by optical pumping and in holding beam direction.