The invention discloses a method for designing a dielectric reflector antenna. The dielectric reflector antenna is composed of a feed source and multiple layers of plane dielectric slabs. Phase modulation is conducted on an array face, wide angular domain beams emitted by the feed source are clustered and reflected to form narrow beams, and therefore high gain is achieved; a periodical master-slave boundary condition modeling and simulating method is adopted; influence on dielectric slab phase modulation by a dielectric constant, the magnetic conductivity, the unit gap, the operating frequency and the incident angle is analyzed, and a corresponding phase modulation curve is obtained when the thickness of dielectric changes; a structure of stacking the dielectric slabs is adopted for phase modulation; a tapered slot antenna is adopted as the feed source. An empty feeding mode is adopted and a design procedure of the dielectric reflector antenna is simplified; the dielectric reflector antenna is formed by stacking the dielectric slabs, no metal patch is arranged, surface loss is reduced, and the efficiency of the dielectric reflector antenna is improved. The dielectric reflector antenna is simple in structure, small in size, low in weight and capable of facilitating processing and installing and has the advantages of being low in loss, high in gain, low in sidelobe and wide in frequency band.