This work focuses on the simulation of an inter-subband GaNAsSb/GaSb based quantum well structures. The effect of nitrogen introduction on the optoelectronic properties such as: bandgap energy, band offset and the inter-subband absorption coefficient of the GaNAsSb/GaSb quantum well structures is investigated using the band anti-crossing model. The study was performed for a small amount of nitrogen ( \(0 \le x \le 5\% )\) . Incorporation of a few percent of N into the GaAsSb host material significantly reduces the fundamental band gap energy, which indicates the very large bandgap curvature commonly found in the III-N-V semiconductors type alloys. At the same time, the inter-subband absorption coefficient and the corresponding emission wavelength were shown to change significantly up on nitrogen incorporation.