Gallium arsenide (GaAs) nanowires are epitaxially grown on an N-type Si (111) substrate by molecular beam epitaxy according to self-catalysis growth mechanism. Testing the grown nanowires by scanning electron microscope, it is found that the nanowires have high verticality and good uniformity in length and diameter. Variable temperature photoluminescence (PL) spectroscopy is used on nanowires. The test results show that the two luminescence peaks P1 and P2 at 10 K are located at 1.493 eV and 1.516 eV, respectively, and it is inferred that it may be the luminescence caused by WZ/ZB miscible structure and the free exciton luminescence peak. These two peaks present red-shift with temperature increasing. The temperature change curve is obtained by fitting the Varshni formula. The variable power PL spectroscopy test finds that the peak position of P1 position is blue shifted with power increasing, but the peak position of the P2 remains unchanged. By fitting, it is found that the P1 peak position is linearly related to power to the power of 1/3, and it is judged that it may be type-II luminescence caused by WZ/ZB mixed phase structure. At the same time, the peak position of the P2 position is fitted and parameter α approximately equals 1.56, therefore P2 is a free exciton luminescence. A Raman spectrum test is performed on the nanowires, and an E₂ phonon peak unique to the GaAs WZ structure is found from the spectrum. It is proved that the grown nanowires possess WZ/ZB mixed phase structures, and the hybrid phase structure of nanowires is more intuitively observed by high resolution transmission electron microscopy.