Nb3Sn and other A15 members have been widely applied in nuclear power, nuclear magnetic reso-nance, and high-energy particle accelerators for their high critical current density (Jc) and upper critical field (Bc2). There have been comprehensive and intensive studies on the applications, the fundamental lattice dynamic and electronic properties, etc., of A15 superconductors. Various reviews on the preparations, structures, and properties have already been written in the last few years. Nevertheless, on account of the large amount of existing facts and views, a coherent view on the relations between the structures and properties has not appeared to unify the facts. This article sketches a multi-scale point of view on the relations between the multi-scale structures and the corresponding properties.