Unlike nanocrystalline (NC) phase, a heterogeneous lamella (HL) composite, consisting of NC and coarse-grain layers, exhibits greatly improved ductility. To understand the fundamental principles governing their high strength and good ductility, we employ a 3D discrete crystal plasticity finite element (CPFE) model to study the spatially resolved deformation fields within each layer and at their interface. Based on an analysis of the distributions of equivalent plastic strain and lattice reorientations within the NC lamella, we show that the heterogeneity of strain concentration, which could potentially lead to shear localizations in the NC layer, has been substantially reduced by the uniform deformation that is characteristic of the coarse-grain lamella. In addition, we find that coarse grains well oriented for multi-slip have an even greater homogenization effect, thereby further increasing the ductility of the entire HL structure. These findings can benefit the design of gradient or heterogeneous structures to achieve superior properties.