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We employ molecular dynamics (MD) simulations to investigate the mechanical behaviors of immiscible polymer interfaces enhanced by block copolymer compatibilizers. We show that the entanglement density at the interface, governed by the Flory–Huggins parameter χ, is critical for mechanical performance. Increasing immiscibility leads to sharper interfaces with reduced interfacial entanglements, resulting in easy chain pullout during tensile deformation and weaker interfacial strength. Adding block copolymer compatibilizers to the blends can switch the failure mechanism from interfacial chain pullout to bulk-phase crazing, substantially enhancing mechanical performance. Although long diblock and tetrablock copolymers only mildly increase the interfacial entanglement density, they can act as stress transmitters across the interface by entangling with chains in the bulk domains. Tetrablock copolymers are particularly effective for strengthening polymer blends by forming loops at the interface, making chain pullout topologically more difficult and promoting energy dissipation through crazing in the bulk regions. Our findings reveal the roles of both entanglement at interfaces and block copolymer architecture in the mechanical properties of immiscible polymer interfaces, which may guide the design of better compatibilizers for enhancing inhomogeneous polymer samples.