The service life of open-die cold extrusion is the most important factor in economic efficiency. To prolong its service life, the design of the die needs a rational structure. Studying the stress of the die wall and its distribution rule is the precondition in cavity die optimization design. Numerical simulation for tube open-die cold extrusion process using finite element software Deform-3D, the distribution of the stress of die wall, the influence rule of the stress of cavity die wall under various kinds of the processing parameter and the optimum range of stress of cavity die wall. The analysis result can take some effective measures to rational design for the die to decrease the die defect, prolong the service life of the die and increase economic efficiency. It can also offer references for optimization design of cavity die.