In this study, we experimentally demonstrated the enhancement of a terahertz (THz) signal generated by a femtosecond laser-filament array in air using a simple experimental setup in which a step phase plate is used to generate multiple parallel filaments. The results show that at a given incident-femtosecond-pulse energy, compared with the case of single filament, the proposed method enhances the THz radiation intensity, and the THz radiation intensity is proportional to the number of filaments. Further, at an incident energy of 5.8 mJ, the THz energy generated by eight filaments is 31.73 nJ and the radiation efficiency is 5.47×10 -6. This simple method can be used to solve the energy saturation problem in the generation of THz radiation through femtosecond laser filamentation in air.