Abstract: This paper analyzes how to obtain higher harmonic component of magnetic field of the Wiggler, proposes a new type of the modified wiggler梩he U form modified Wiggler, optimizes the parameters of the modified Wiggler, discusses the trajectory of the electron and the spontaneous emission spectrum of the modified Wiggler. To prove the theory, a model including six periods had been made, and the distribution of the field of the model had been measured. The result of measuring verifies the theory on the whole.