Core-shell nanoparticles of Fe₃O₄/PAMAM/ZnO/TiO₂ and Fe₃O₄/PAMAM/TiO₂ were prepared by hydrothermal method with polyamidoamine (PAMAM) as template and isolation layer, while the construction mechanism and performance of which were investigated. The mophology, size, structure and proporties of these particles were characterized by HRTEM, EDS, XRD, SQUID and UV-Vis measurements. The results show that core-shell nanoparticles present clearly structure composed of magnetic core and shell, which were stacked with nanoparticles less than 5 nm in diameter, leading to high saturation magnetization and MB-adsorption rates. Althouth the interfacial contact area of core and shell was reduced by PAMAM isolation layer, trace electrons Fe²⁺ at the inerface could migrate into the TiO₂ shell through the residual interfacial contact area, and then combine with the holes in shell, which brought the narrowing of shell band gap and the red-shifting of the absorption spectrum and thus the decreasing of catalytic activity. As for Fe₃O₄/PAMAM/ZnO/TiO₂, the thicker PAMAM and ZnO layers cutted off the way of electrons migration to the TiO₂ shell. The heterogeneous structure of ZnO/TiO₂ facilitated the separation of the photogenerated electron hole pairs in shell. The new interface electronic states brought further red-shifting of the the absorption spectrum, higher utilization ratio of visible light, and therewith resulted in higher catalytic activity. The magnetic recovery and MB-degradation rate of Fe₃O₄/PAMAM/ZnO/TiO₂ are 93.8% and 90.8% respectively after being recyced for 5 times.