Intelligent grouping method divides a large amount of parameters into different groups intelligently according to the difference of data which is significant between groups but no significant in the same group,so as to find out the key factors affecting defects.This paper analyses the small black point defect found in the low C/ Mn steel and the edge of container board using the method.Results show that chemical content and heating process of hot rolling of plates are the major factors which affect the probability of arise sing little black point defect in the edge of plates,and it is benefit to low probability of that lowing temperature of plate exiting of the furnace and lower raising rate of temperature.