Wiggler is an important part of free-electron lasers (FEL). According to the calculation analysis and the over-all requirement of the FEL, the consideration in designing the wiggler is given, a simulation device with a few periods is developed and the effect of magnetic field intensity on magnetic gap, period, size, and material are measured, and the sinusoidal distribution of the magnetic fleldis investigatied. It is concluded that the design and the device can be used in FEL.