Cognitive diagnosis (CD) and automated item generation were important developing directions in modern psychology measurement. To combining with both areas was a major topic to explore. Illustrated with ordinary mathematic problem solving, this paper investigated the methodology and algorithm of automated item generation in CD. Findings showed: (1) Item parameters generated by computer were highly consistent with the parameters in mode; (2) The testing characteristics of different items generated by the same item mode were almost the same; (3) The abilities consequences obtained by two different auto-generated test were highly correlated (r=0.811), and cognitive diagnosis obtained by the same tests were highly consistent. All these verified that the methods and algorithm of automated item generation in CD were feasible, and they could work efficiently, which provided a mechanic reference and support of the automated item generation in CD area.