Grain size is one of the most important parameters affecting material strength and ductility. When a homogenized grain size model is employed (such as in the Hall-Petch model), it disregards the effects the heterogeneous nature of the microstructure (grain size spatial distribution, grain shape) may have on strength and plastic flow. In this work, we employ a multi-scale approach to study the effect of heterogeneous microstructure containing nano and micron size grains. This is based on dislocations analysis that includes discrete dislocation dynamic (DDD), continuum dislocation dynamic (CDD) and a visco-plastic self-consistent (VPSC) model. A combined strain-gradient and stress-gradient theory is implemented into the framework by means of a heterogeneous grid. Different distributions of nano-layers are imbedded into an otherwise homogenous microstructure resulting into a gradient nanomicrostructure. Several simulations of microstructures with various grain size spatial distributions and different number of nano-layers are investigated, and the results are compared to their counterpart homogenized structures.