Expandable cased-hole liners is to solve the sealing problem of level six multilateral wells. It is a trigeminal expandable tube which is usually prefabricated on the ground and re-expanded when placed in the proper position. In this paper, the trigeminal expandable tubular compression molding process of the pre-forming stage is mainly studied. In this compression process, both sides of the branch pipe should be compressed to a certain shape in order to successfully enter the main borehole; meanwhile, we want to make sure that failures such as rupture do not occur in the subsequent expansion process. According to the theory about sheet metal bending forming process, three different shapes of the mold are designed to control the cross-section shape of the compressed trigeminal expandable tube so that it meets the application requirements. Rack-shaped cross-section is finally selected as a reference of the best through simulation of compression process and comparative analysis of simulation results. At last, field tests show that this cross-section shape is compatible with the theoretical and simulation results.