Abstract: In split Hopkinson pressure bar(SHPB) test,the stress uniformization process in specimens was studied.The results indicate that the stress non-uniformity obviously appeared at the beginning of dynamic compression,which mainly behaved as follows: the level of stress was different at the two bottoms of the specimen and the tenor of stress-time was non-synchronizing along with large vibration.In the course of time,the stress distribution in the specimen gradually got uniformed.The non-uniformity degree of stress distribution in the specimen was judged by absolute stress unevenness α(t).The curve of α(t)-t had an obvious kinkpoint M.It is suggested that the correspondent time of kinkpoint M is the time needed for stress distribution uniformization in the specimen.