Despite the highly developed level of the silicon technology, efficiency of silicon-based photon devices is limited by material properties. In contrast, III-V materials are mostly applicable to make such type of devices as well as  fabricating them in nanowire (NW) form provides compatibility with silicon technology. GaP(NAs) is a useful material system for optoelectronics because of tunable bandgap with controllable directivity and high refractive index. The  eigenmodes of the Fabry-Perot resonator based on GaP NWs have been investigated. The simulation results showed that raise in diameter leads to the increase in the number of optical modes having different light distribution due  to transverse mode type. Quality factor analysis shows growth in its values with the increase in structures’ diameters.