In this study, electroless $Ni-Fe_3O_4$ composite plating on polyester fabric modified with 3-aminopropyltrimethoxysilane (APTMS) was investigated under ultrasonic irradiation. Effects of deposit weight on microstructure and properties of $Ni-Fe_3O_4$ composite coating were studied. Surface morphology, chemical composition and state, crystal structure of the electroless $Ni-Fe_3O_4$ composite plated polyester fabric were characterized by SEM, EDX, XPS and XRD. Magnetic properties, electrical resistivity and electromagnetic interference (EMI) shielding effectiveness (SE) of $Ni-Fe_3O_4$ plated polyester fabric were also evaluated. The presence of co-deposition of $Fe_3O_4$ in Ni coating on the polyester fabric is demonstrated by an XPS analysis. At a higher deposit weight, there is an increase in particle size and saturation magnetization, and a decrease in electrical resistivity with respect to the rise of deposit weight, respectively. As the $Ni-Fe_3O_4$ weight on the treated fabric is $32.90g/m^2$, the EMI SE of the $Ni-Fe_3O_4$ plated polyester fabric arrives 15-20 dB at frequencies that range from 8 to 18 GHz. The results indicate the $Ni-Fe_3O_4$ plated polyester fabrics are used as super-paramagnetic, conductive and EMI shielding materials.