In this study, the interfacial stereocomplex crystallites (i-SC) is fabricated and used to regulate the phase morphology of immiscible polymer blend from sea-island to co-continuous structure. i-SC is created by reactive compounding of poly(L-lactide) (PLLA) and poly(vinylidene fluoride) (PVDF) in the presence of the reactive poly(D-lactide) PDLA-based compatibilizer. As the grafting reaction between PLLA and compatibilizer occurred during blending, the stereo-complexation of PLLA/PDLA formed and aligned simultaneously along the PVDF-PLLA interface, generating a relatively hard interfacial-layer between two phases. i-SC can not just serve as conventional compatibilizer by selectively entanglements of grafts with corresponding miscible polymer. The existence of hard crystal fractions in i-SC effectively reduce interfacial curvature, and thereby facilitate the formation of co-continuous microstructure. It can be inferred that the formation and stability of the plat interface are directly attributed to steric protection of i-SC between phases: i-SC is capable of providing a stronger bending energy than conventional compatibilizers to balance the interfacial energy, suppressing break-up of fibers and thus inducing the formation of flat interface. i-SC should be a new interfacial modifier in adjusting phase morphology of polymer blends.