Abstract: In view of the phenomenon that larger vibration amplitude results in a highly reduced UT reliability about thin Wall and small diameter Ti Tubes and based on study and experimentation,it′s proved that if position variation of the tube as related to probe position does not exceed certain range,UT detection sensitivity will remain relatively stable.The paper provides the varying quantity information related to formula calculation& experiment method and experiment datas,The actual application result proves that the method is effective and easy to realize.