Forced vibration and liquid corrosion are important reasons for last stage blade failure in steam turbine. In order to improve reliability of blades in wet steam stages, the dynamic stress and the liquid-solid impact stress of blade were analyzed firstly, then Neuber’s rule, rainflow counting method and improved cumulative damage rule were introduced to develop a new model to evaluate service life of last stage blade. Many factors such as manufacturing quality, metal quality and operation status were considered, so it is more reasonable for service life assessment of last stage blade. At last, the service life of a last stage blade of 680mm was analyzed and the result approximates the practical service life. It is shown the new fatigue model can give some significant data and is usable for engineering application.