A novel method for writing long fiber Bragg grating (FBG) with arbitrary multi-wavelength and chirp at the same place of a fiber by using a phase mask is presented. An experimental equation is derived for Bragg wavelength, and the Bragg wavelength is found to be a function of the distance between the fiber and the phase mask. The chirp of the overlapped FBG is decided by the angle between phase mask and fiber. A multi-wavelength FBG with 4, 8, 16 channels has been written by using a unique phase mask.