For polymorphic polymers, the effect of interfacial modification on the interfacial property of the polymer composites still remains poorly understood. Here, we proposed a novel diffusion strategy of nucleating agent's (NA) interfacial aggregation, endowing the polypropylene (PP)/polyamide (PA) interface with high nucleating activity to trigger the preferential growth of well-organized transcrystalline layer perpendicular to the interface. By adjusting the kinds of the added NAs, the modifications of the transcrystalline layer were tailored so that the contributions of the interfacial polymorphs to the interfacial strength were explored. The results showed that due to lamellar slippage of loose beta-crystals accompanied by beta to alpha transformation, the beta-transcrystalline layer exhibited more superiority in perfecting the interfacial properties over alpha-one. When the thickness of the transcrystalline layer was 33.7 mu m, the PP/PA system with the beta-transcrystalline layer was characterized by the shear strength of 3.26 MPa, higher than 2.83 MPa of the PP/PA system with the alpha-layer.