Electrically conductive polymer composites (CPCs) have been applied extensively in many fields such as electronics, wearable sensors and antistatic agent. It is still challenging to develop CPCs with a low percolation threshold and high electrical conductivity. Here, highly electrically conductive polystyrene (PS) composite with a fiber-based segregated structure is prepared by carbon nanotubes (CNTs) decoration onto the electrospun PS fibers, followed by hot press at a proper temperature. In the electrically conductive PS composite, the CNTs are segregated at the interface among the fiber-shaped matrix, and the one-dimensional fiber possessing the merit of a large aspect ratio, which facilitates the formation of conductive network. The percolation threshold is calculated to be 0.084 vol%, and the electrical conductivity of the CPC reaches 83.3 S/m when the concentration of the CNTs is 1.5 vol%. If the hot press temperature is much higher than the glass transition temperature of PS, the fiber-based segregated structure would be destroyed, increasing the percolation threshold while decreasing the conductivity of the composite. The fiber-based segregated structure provides a new and versatile route for the rational design and preparation of CPCs with a low percolation threshold and high conductivity.