The invention discloses a tool for an expandable casing in an open hole section, which is applied to construction for the expandable casing in the open hole section in petroleum well completion. The tool for the expandable casing in the open hole section is mainly divided into a hydraulic cylinder body assembly, a piston rod and expandable cone assembly, as well as an expandable tube and anchor assembly. The tool for the expandable casing in the open hole section has the following advantages: construction work for an open hole system in an expandable tubular technical system can be finished; after the tool system is applied to perform the construction work, the purpose of disposing complex conditions in a downhole can be achieved, and the normal performance of a subsequent well drilling process can be ensured, so that well drilling risks and accidents can be effectively disposed, the safety and the reliability of the well drilling process can be improved, and the well drilling speed can be increased; moreover, the use of raw materials is reduced, thus decreasing the costs of well drilling and well completion.