For the beam of a laser diode, the source size is very small and the light beam has a large divergence angle. In addition, in the nonparaxial region the optical field distribution is considerably different from that given by scalar theory. The nonparaxial theory of vector beams should be used to describe these fields. A mathematical model to describe the far-field distribution of the nonparaxial laser diode beam is presented. The laser diode beam propagation is studied by the vector Rayleigh diffraction integrals, and the stationary-phase method is employed to find the asymptotic expansion of the diffraction integral. The propagation expression for nonparaxial laser diode beam is given. The calculated results show the vectorial theory model is more precise in the nonparaxial region.