Pivotal parameters and restricted condition of the grating-size-limited compressor in an ultra-short, ultra-intense laser system are analyzed, and three basic parameters are obtained. An optimal method for compressor to output a maximal pulse energy is developed, and the maximal output pulse energy of the grating-size-limited compressor is given. Compared with the traditional circular beam method, an advanced elliptical beam method is presented, which could be used to output much higher pulse energy, a smaller spot size and a larger focal intensity. Using numerical simulation, the maximal output pulse energy of the 500 mm grating compressor based on the circular beam and the elliptical beam are calculated separately. The results show that the 500 fs, 500 J, 1 PW pulse can be obtained without using tiled grating technology if elliptical beam method is used.