During this work, we have studied the structural and optoelectronic properties of an epilayer of GaAsN grown by molecular beam epitaxy on GaAs substrate. The X-ray diffraction has been used to determine the nitrogen content in the studied sample and it had been found to be 1.2%. The optoelectronic properties of this sample's structure has been studied by the mean of the CW-photoluminescence and time-resolved photoluminescence. The CW-PL spectrum consists of two peaks. The principal one is located at 1.303eV, associated with the band to band transition. This transition is confirmed by a numerical calculation of the band gap based on the anti-crossing model. The second peak, located at 1.162eV, is associated to a deep energy level(within the band gap)..