Abstract: In order to simplify the complicated theory and calculation about arrayed wave-guide gratings(AWG),a simple analysis theory method is provided for the design of AWG,in which the gaussian approximation of the field distribution of the mode in an wave-guide,effective index method and Marcatili method were adopted to analyze the optical wave-guides,without regard to the dispersion of the slab wave-guides.Based on the above approximation,a simple and practical AWG calculation method is obtained.