The concept of Digital Twin (DT) was presented to open the research on the image of reality in virtual digital space-time. The DT of aircraft structure is implemented in this paper, which is a typical case of computational mechanics. There are five stages including design, manufacture, operation, maintenance and decommissioning to expound. The development idea and method of establishing DT from solid structure are analyzed, the sublimation of computational mechanics from numerical simulation and simulation stage to DT stage is discussed, and many problems to be solved in the whole life cycle process are revealed. The eight key techniques of DT are extracted: motivation, knack, way, coupling, dynamic, transformation, advancing and level. The self-deepening and lateral migration of DT development in computational mechanics are prospected from two aspects in the professional depth and horizontal and vertical extension, and so on.