Abstract: In this article, a brief account of the status quo of domestic blade failure cases, together with some description of ideas about untuned blades is given. For untuned blades, a new paramenter, Safety Ratio Ab, which can better evaluate the vibration strength of blades than the formerly used Steam Bending Stressσsb is demonstrated; a new safety criterion in the form of a demarcation curve for allowable [Ab] VS order of harmonics K is established, after analysing operating data of 570 turbinestages, some features of the new criterion, such as adoption of bending stress in the direction of vibration to evaluate Ab and introduction of "transition zone"; its application in clarifying causes of serious blade failures. For tuned blades, a new criterion consisting of allowable dynamical frequency margin and relevant [Ab] values is established on the basis of criteron for untuned blades and thru theoretical analysis combined with abundant practical experiences.

Key words: drivability, mMPC (multiple model predictive control), low frequency longitudinal vibration, TTRP(Through-The-Road Parallel) HEV（hybrid electronic vehicle)