A fiber grating structure with cladding radius as sinusoidal function along the grating length is introduced. The transmission properties of the this type grating was studies on the basis of the transfer matrix theory. Compared with linearly chirped fiber grating, the fiber grating exhibits a Box spectrum with steep edges and high reflectivity when tension is applied to it. With the tension increasing, the center wave length in the grating reflecting spectrum will move toward the long wave direction and the reflecting bandwidth is greatly widened.