A new preparation method of the double-side modulation Bragg waveguide grating by one step is proposed. In the structure, spatial modulation of the waveguide grating is achieved by periodically changing the width of the waveguide. The advantage of this structure is that waveguide and grating are achieved at the same time by using a simple waveguide fabrication technology. According to transfer matrix theory, the relationship between the reflection spectrum characteristics of this structure and the waveguide width, the difference of waveguide width, the duty cycle of gratings, the changes of the waveguide in the shape is studied. Results show that 3 dB bandwidth of grating with double-side modulation is wider than that of grating with corrugated modulation. At the same time, the maximum reflectivity is increased slightly. When the difference of waveguide width is fixed, the maximum reflectivity and bandwidth decrease while the waveguide width increases. In addition, when the waveguide width is fixed, the maximum reflectivity and bandwidth increase while the waveguide width increases. When both the waveguide width and its difference are both fixed, the maximum reflectivity and bandwidth achieve these maximums at the duty cycle of 1/2. Furthermore, the bandwidth can be controlled by changing the duty cycle when the difference of waveguide width is large enough. And the waveguide shape change has a small impact on the reflection spectrum properties of waveguide grating.