In this paper, the optical properties of the GaP nanowires-based directional X-coupler are investigated for the design and further fabrication of a passive nanophotonic device. Results of numerical calculations demonstrate how the coupling length, nanowires diameter, and the gap between them influence the spectral composition of the output signals. By optimizing these geometric parameters, efficient subwavelength directional X-couplers based on GaP nanowires can be fabricated for light control in photonic circuits.