The field emission current densities from AlxGa1 - xN are theoretically calculated as a function of stoichiometry. The material parameters of AlxGa1 - xN are obtained as weighted averages of those of AlN and GaN. The Poisson equation is first solved to obtain the energy band diagrams as a function of the composition x. The transmission coefficient through the tunneling barrier is numerically calculated using the fact that the Airy function is the exact solution of Schrodinger's equation for a linear potential. By evaluating the energy-dependent integral on the band structure-dependent surface that is given by projecting the energy ellipsoid on the emission surface, we obtained the field electron energy distribution j(E). The calculated emission current j shows a strong dependence of the field emission on the stoichiometric composition x. The obtained Fowler-Nordheim plots exhibit different field dependent structures in the low and high field regimes. It is also found that the carrier concentration dependence of j is not pronounced for low fields but becomes significant for high fields.