Based on the current problem of the inability of the extension arm to balance the relationship between small mass and large-scale, this paper proposes a new type of extension arm with a grid cylinder structure, which includes four aspects: the extension arm body, the guiding system, the locking system, and the control system. The structure is simple and can effectively reduce the mass of the main structure of the extension arm. At the same time, a timing release mechanism is designed to enable the extension arm to be unfolded sequentially. Finally, a virtual prototype is established in Mechanical dynamics simulation software and the unfolding process of the extension arm in different unfolding modes is analyzed to verify the feasibility of the extension arm unfolding and the relative stability of sequential unfolding compared to synchronous unfolding.