Abstract: The styrene-acrylic emulsion used to prepare waterborne damping coatings needs to further increase the damping factor and broaden the effective damping temperature range. In order to improve the damping performance of styrene-acrylic emulsion, oleic acid (OA) modified nano-Fe₃O₄ (OA-Fe₃O₄) was used as the coated filler to prepare Fe₃O₄/poly(styrene acrylate) (Fe₃O₄/P(St-2-EHA)) composite damping emulsion via miniemulsion polymerization. The composite emulsion and its latex film were characterized by FTIR, XRD, TEM, SEM, DLS, TG and DMA. The effects of copolymer composition, surface properties and content of nano-Fe₃O₄ on the structure and performance of the emulsion and latex film were studied. The results show that the direct agglomeration of OA-Fe₃O₄ nanoparticles is weakened, and its dispersion in the composite emulsion is significantly improved. When the mass ratio of monomer St to 2-EHA is 5∶5, the obtained P(St-2-EHA) latex film has the highest loss factor (tanδ) peak (1.926). When the mass ratio of OA-Fe₃O₄ to the total mass of St and 2-EHA is 10wt%, the obtained Fe₃O₄/P(St-2-EHA) composite latex film has the best performance. Its tanδ peak value and effective damping temperature range width are 2.066 and 59.2℃, which are better than pure P(St-2-EHA) latex film and composite latex film prepared by blending method. Its water absorption rate is 3.4% and 10.4% lower than the latter two respectively. And the initial thermal decomposition temperature is higher, with the thermal stability improved.