Abstract: By controlling the amplitude value of strain during the process of loading,taking 45 steel with precut V-notch as the subject investigated,studying the notch effect on fatigue life of round bar,and applying the knowledge of the life prediction theory on ductile materials in low cycle fatigue,the amended Manson equation and algorithm of the estimating-life model was proposed.The predicted curves and strain-life curves well agree with experimental data for medium carbon steel.