Abstract: In order to solve the max freezing technical difficulty of the single ultra thick clay in the auxiliary shaft of Zhangji Mine, a site measurement was conducte d on the stress status of the freezing shaft wall, the freezing pressure, ring reinforced bar of the shaft outer liner, vertical reinforced bar stress and other data were obtai ned and the analysis was conducted on the data.The study showed that the increasing speed of the freezing pressure of the ultra thick clay layer was fast and would re ach the max value about 5 days.The freezing pressure would be born mainly by the ring reinforced bar of shaft outer liner.The initial freezing pressure would be increas ed by the thickness of the clay layer.In combination with the site measured data of Zhangji Mine, a linear regression analysis was conducted and a linear regression eq uation of the max freezing pressure with the stratum depth was Pmax=0.019H-2.831.