Abstract: According to the problem of LVDT connecting rod of high pressure control valve has broken many times during the operation of 600 MW turbine units, this paper analyzes the reasons from the aspects of macroscopic fracture, chemical composition, metallographic struct-ure, working condition, the results show that high pressure control valve and its LVDT have great vibration in operation, so that we finally confirmed that fatigue cracking occurs at the stress concentration part at the root of the connecting rod thread.The existing problems and hidden dangers were successfully eliminate by optimizing steam turbine valve flow characteristics and upgrad-ing LVDT connecting rod materials, the safety and reliability of unit operation.