The arrayed waveguide grating (AWG) has greatly prospective in optical communication as a wavelength filter. Crosstalk is one of the most important factors which block the wide use of AWGs. In order to reduce the crosstalk of an AWG, a new method was proposed and studied in this paper. In this method, the output minimum of a channel is located at the center of the waveguides of other channels and there is no sidelobes of the channel in the waveguides of other channels in the mean time by adjusting the free spectrum range (FSR) of AWG, foca length of Rowland circle and the number of the waveguide array. Thus the crosstalk of an AWG, pecially the adjacent crosstalk can be reduced greatly. Numerical approaching of 1×16 AWGs with different FSR by beam propagation method (BPM) shows the adjacent crosstalk can be reduced about 5.7 dB by this method.