Abstract: View of the mudstone collapse encountered in Bachu and Sangtamu formations in deep sidetracking wells of Tahe Oilfield,the solid expandable tube with 5.5 inch OD was selected to seal the mudstone mechanically.According to the theory of elastoplasticity,finite element numerical simulation was adopted to study the expansion characteristics of the solid expandable tube,the expansion ratio,yield strength,friction coefficient and the impact on the expansion force by expansion cone angle were analyzed.The expandable tube was used in Well TK6-463CH of Tahe Oilfield,which was designed with an expansion cone angle of 10°,expected expansion force of 603-607 kN,with a simulation error of less than 8%.The results show that the method is feasible,providing reference for expandable tube design and operation in deep well sidetracking.