Abstract: About a coil being charged with a sine-alternation,there is a sine-walking-wave magnetic field.The distance between N and S of the field and the speed of the walking wave all can be regulated by changing the frequency of the sine-alternation.We get the result that the relativistic electron can get off shorter scattaning wavelength from the wiggler,the energy factor can be changed.Therefore the wiggler can be benefitical to the development of shorter wavelength and can contribute to the realization of the miniaturization of FEL.