Based on coupled-wave theory, the fundamental principle of angular multiplex in volume holographic storage is discussed. The influence of the different beam path geometric arrangements, such as symmetrical write, unsymmetrical write and near-plane write, on the angular multiplex density was analyzed. Considering the limitation of total reflection about storage material, the equation of maximum angular multiplex density was derived. The theoretical analysis and digital simulation results indicate that the unsymmetrical incident light path has a higher angular multiplex density than the symmetrical one, and the angular multiplex density of the near-plane incident beam path is the best and is directly proportional to the reference beam.