Abstract: This paper reports the process in which a related equation between the nodulizing level of cast iron and the three characteristic values of the thermal analysis curves,i. e. the releasing energy in the eutectic solidification, the time of the eutectic solidification and the lasting time of the violent eutectic transformation, can be set up by means of regr-ession analysis. Then the nodulizing level of ferrite ductile iron melted in cupola may be quickly determined within three and a half minutes after the sample has been poured. According to "JB 1802-76" classification, the error of this method is only one level.