Beam splitting of low-contrast rectangular gratings under second Bragg angle incidence is studied. The grating period is between λ and $2\lambda$ . The diffraction behaviors of the three transmitted propagating orders are illustrated by analyzing the first three propagating grating modes. From a simplified modal approach, the design conditions of gratings as a high-efficiency element with most of its energy concentrated in the $-2\mathrm{nd}$ transmitted order $(\sim 90\%)$ and of gratings as a $1\times 2$ beam splitter with a total efficiency over 90% are derived. The grating parameters for achieving exactly the splitting pattern by use of rigorous coupled-wave analysis verified the design method. A $1\times 3$ beam splitter is also demonstrated. Moreover, the polarization-dependent diffraction behaviors are investigated, which suggest the possibility of designing polarization-selective elements under such a configuration. The proposed concept of using the second Bragg angle should be helpful for developing new grating-based devices.