The multiscale modeling has developed to investigate size-dependent plasticity by coupling conventional continuum crystal plasticity finite element (CPFEM) with a discrete defect (DD) modeling. While the detailed defect microstructure and short-range interaction is handled by DD framework, the long-range elastic interactions with image stress field are calculated by CPFEM (using commercial package(ABAQUS) with user-subroutine), accounting for complex boundary conditions. The proposed model could account for complex multi-physical phenomena, which would play an important role in obtaining a fundamental understanding of deformation mechanism at small scale. Applications of developed concurrent coupled model includes dislocation nucleation at a crack tip, nanoindentation, hydrogen embrittlement at submicron length scale. The developed model will shed light on fundamental investigation of “defect-controlled” mechanical behaviors in crystalline materials, such as plasticity and damage and fracture.