<p>Spatial confinement of block copolymers can induce frustrations, which can further be utilized to regulate self-assembled structures, thus providing an efficient route for fabricating novel structures. We studied the self-assembly of AB di-block copolymers (di-BCPs) confined in Janus spherical nanocavities using simulations, and explained the structure formation mechanisms. In the case of a strongly selective cavity wall, all the lamella-forming, gyroid-forming, and cylinder-forming di-BCPs can form interfacial frustration-induced Janus concentric perforated lamellar nanoparticles, whose outermost is a Janus spherical shell and the internal is a sphere with concentric perforated lamellar structure. In particular, Janus concentric perforated lamellar nanoparticles with holes distributed only near the equatorial plane were obtained in both lamella-forming and gyroid-forming di-BCPs, directly reflecting the effect of interfacial frustration. The minority-block domain of the cylider-forming di-BCPs may form hemispherical perforated lamellar structures with holes distributed in parallel layers with a specific orientation. For symmetric di-BCPs, both the A and B domains in each nanoparticle are continuous, interchangeable, and have rotational symmetry. While for gyroid-forming and cylinder-forming di-BCPs, only the majority-block domains are continuous in each nanoparticle, and holes in the minority-block domains usually have rotational symmetry. In the case of a weakly selective cavity wall, the inhomogeneity of the cavity wall results in structures having a specific orientation (such as flower-like and branched structures in gyroid-forming and cylinder-forming di-BCPs) and a perforated wetting layer with uniformly distributed holes. The novel nanoparticles obtained may have potential applications in nanotechnology as functional nanostructures or nanoparticles.</p>