Alzheimer's disease (AD) is pathologically characterized by cerebral amyloid β-protein (Aβ) aggregation, neurofibrillary tangles and progressive cognitive deterioration. There is an urgent clinical demand for targeted therapeutic agents against AD, whereas the blood-brain barrier (BBB) acts as a critical physical barrier that blocks over 98% small-molecule drugs and nearly all biomacromolecules from entering brain parenchyma. Nanomedicine-based drug delivery systems (NDDSs) with tunable physicochemical properties can cross the BBB via multiple transcytosis pathways including adsorptive-mediated, receptor-mediated and transporter-mediated routes, opening a promising avenue for targeted AD treatment. A core academic viewpoint proposed herein is that robust in vitro endothelial penetration of nanocarriers cannot guarantee effective accumulation in brain target cells. Comprehensive evaluation of BBB-crossing delivery efficiency should not merely rely on in vitro permeability tests, but cover the full multi-step transcytosis cascade, cellular tropism in brain tissues and in vivo therapeutic outcomes. This review systematically sorts out diverse nanoplatforms applicable to BBB penetration for AD intervention. Inorganic nanomaterials such as gold and ceria nanoparticles possess large specific surface areas and intrinsic antioxidant capacity, which eliminate reactive oxygen species and hinder Aβ fibrillization. Liposomal formulations and solid lipid nanoparticles exhibit superior biocompatibility with biomimetic phospholipid bilayer architectures, capable of co-loading hydrophilic nucleic acids for Tau regulation and lipophilic Aβ inhibitors; relying on receptor-mediated transcytosis, they achieve sustained drug retention in the brain. Polymeric nanocarriers including nanogels and polyamidoamine dendrimers enable multi-target combinatorial therapy, and can be engineered to release cargo in response to inflammatory microenvironments, thereby suppressing excessive microglial activation and protecting neuronal mitochondria. Beyond conventional nanocarriers, this work elaborates two cutting-edge BBB-crossing delivery platforms: biomimetic nanosystems and metal-organic frameworks (MOFs). Biomimetic nanoparticles camouflaged with erythrocyte, platelet or macrophage membranes, as well as natural exosomes, evade immune clearance, prolong systemic circulation and inherently home to inflammatory lesions. Serving as "nano-decoys", they neutralize Aβ neurotoxins and remodel cerebral inflammatory microenvironments simultaneously. MOFs feature high porosity and customizable pore channels for co-delivery of multiple therapeutics, and can be integrated with near-infrared photothermal and photooxidation modalities to facilitate focal brain lesion therapy. This review highlights a transformative paradigm shift in the field of BBB-targeted AD therapy: research focus has shifted from simply maximizing cerebral drug penetration toward active modulation and functional restoration of the BBB. Impaired BBB transporters intrinsically impede endogenous Aβ clearance. Accordingly, BBB-regulating nanocarriers are designed to remodel the low-density lipoprotein receptor-related protein 1 (LRP1) trafficking cascade, redirecting endocytic vesicles from lysosomal degradation to non-degradable transcytosis and restoring the intrinsic Aβ efflux capacity of the BBB. Distinct from conventional strategies that only exert local lesion inhibition, this systemic clearance strategy eliminates cerebral Aβ deposits by accelerating peripheral excretion.