Based on the electromagnetic field theory, the optical signal transmission characteristics in input/output waveguides, slab waveguides and arrayed waveguides of the arrayed waveguide grating (AWG) multi/demultiplexer are analyzed. The relationship between the physical parameters such as geometry sizes and relative refractive index in AWG multi/demultiplexer and the optical signal transmission characteristics are discussed. This theoretical study can be used for optimizing the design and improving the performance of the AWG multi/demultiplexer. Based on the electromagnetic field theory, the optical signal transmission characteristics in input / output waveguides, slab waveguides and arrayed waveguides of the arrayed waveguide grating (AWG) multi / demultiplexer are analyzed. The relationship between the physical parameters such as geometry sizes and relative refractive index in AWG multi / demultiplexer and the optical signal transmission characteristics are discussed. This theoretical study can be used for optimizing the design and improving the performance of the AWG multi / demultiplexer.