It is significant of the flat spectral response arrayed waveguide grating in practical application. Flat spectral response arrayed waveguide grating is systematically studied. Tapers with exponential type are introduced into input waveguides, output waveguides and arrayed waveguides. Optimal design is achieved by changing the shape and size of the tapers. Firstly, the output spectral characteristic is discussed theoretically for tapers with exponential type and the relational expressions of the structural parameters are given. It is illustrated that the characteristic of the tapered input waveguides is the main factor that affects the output spectrum and that the tapered arrayed waveguides and the tapered output waveguides have a certain impact on the output spectrum. Secondly, numerical simulation method is used to simulate the output spectrum and to optimize the structure. Trend and regularity about flat spectral response affected by the structure of tapers are concluded. Simulation results show that the 1 dB passband width is bigger than 50% of the channel spacing, Insertion loss decreases from 5.2 to 4.0 dB, crosstalk is less than -30 dB. Finally, the experimental results are given, insertion loss reduces 0.87 dB, crosstalk decreases 3.67 dB, and 1 dB bandwidth increases 0.1 nm with an increase of 54.7%. Experimental results show that the introduction of tapered waveguides with the exponential type improves the spectral properties of the arrayed waveguide grating device.