Poly(p-phenylenetere phthamide) fiber is a high-performance synthetic fiber whose reinforced composites are widely used for their advantages of high strength and lightweight. However, the further potential usage of poly(p-phenylenetere phthamide) and its reinforced composites is limited in areas such as antistatic materials, conducting materials, and electromagnetic shielding materials due to their high electrical insulation. To improve the electrical conductivity, an online polymerization coating technology was used to manufacture conductive poly(p-phenylenetere phthamide)/polyaniline composite yarns continuously. The conductive poly(p-phenylenetere phthamide)/polyaniline composite yarns’ structure and properties such as surface morphology, electrical conductivity, Fourier-transform infrared spectroscopy spectra, thermogravimetric performance, and mechanical properties were studied in details. Then, three kinds of multiaxial composites were prepared by using the conductive poly(p-phenylenetere phthamide)/polyaniline composite yarn as the reinforcement and unsaturated polyester resin as a matrix, and the electromagnetic shielding performance of the composites was measured. The results indicated that the conductivity of conductive poly(p-phenylenetere phthamide)/polyaniline composite yarn can reach to ~160 S/m. The thermogravimetric performance of poly(p-phenylenetere phthamide) was reduced after conductive treatment. The mechanical properties of the composite yarns, such as the breaking strength and elongation, remained unchanged when the oxidant concentration was lower than 0.6¿mol/L and decreased with the increase in the oxidant concentration. The electromagnetic shielding composites show a certain anti-electromagnetic radiation capability, and the shielding effectiveness value increased with the axial number and density of the conductive poly(p-phenylenetere phthamide)/polyaniline composite yarns. For the tetra-axial composite with a conductive yarn density of 37 yarns per inch, the average shielding effectiveness value in the frequency range of 100¿MHz to 1500¿MHz can exceed 22¿dB.