Abstract: The wavelength of the waveguide of array antenna can be varied by mechanically adjusting the broadside size of the waveguide.Thereby adjusting the broadside size of the waveguide can achieve the same effect of beam scanning by varying feeding microwave frequency. In this paper, the beam scanning characteristics of narrow edge radiation waveguide traveling wave array antenna is analyzed. The maximum beam scanning range with the variation of the broadside size of the waveguide of array antenna under different spacing distance between adjacent radiation slots is analyzed. We designed an X-band waveguide slot array with variable broadside size of waveguide. We designed the beam scanning range point to waveguide feeding end and avoided array normal radiation (the radiation efficiency in normal radiation is low). The continuous beam scanning range is 29°. In the beam scanning range, the gain drop is less than 3 dB.The radiation efficiency is greater than 62%. The slot width of array is 3 mm, the waveguide length is about 1 m, and the number of slots in single waveguide is 40. The capacity of high power microwave of a single waveguide slots antenna can achieve 70 MW.