It was described that the steel crane beam system with crane ′ s lift capacity being no more than 20t, and whose beam span being no larger than 12m. It was also conducted that numerical descriptions of the lectotype for the crane beam. 论述了吊车起重量不超过20t的中轻级工作制度的吊车和吊车梁跨度不超过12m的钢吊车梁体系,并对吊车梁的选型作了一些数字化的细说。