Abstract: Positioned thickness measurement is a simple, reliable, universal and effective means of monitoring to equipment and pipeline corrosion. The main manufacture difficulties of positioned thickness measurement in high temperature by sound velocity were analyzed. The method of adjusting sound velocity was proposed. The advantages and disadvantages of the two methods were analyzed and the testing block used was introduced. The heating method of high temperature block was recommended. Testing on-site showed that the sound velocity method was effective to measure the thickness.