The present invention relates to a grating and a method, belongs to the optical communication technology field, and especially relates to an array waveguide grating of reducing kerf additional optical loss and a method for reducing kerf additional optical loss of an array waveguide grating. The array waveguide grating comprises an input waveguide, an input flat area, an array waveguide, an output flat area and an output waveguide; and the flat areas have period sectional-type waveguide areas. The speckle sizes of light wave is changed from small to big and then from big to small when the light performs propagation in the period sectional-type waveguide areas, the kerf is formed on the period sectional-type waveguide areas on the flat areas, and the additional optical loss generated by the kerf is low to reduce the requirement for the kerf width, reduce the kerf technology difficulty and improve the kerf yield.