It is all known that the BN sheet is a nonmagnetic wide-band-gap semiconductor. Using Density Function Theory (DFT), the lattice parameters of Cr doped BN sheets were optimized, which were still kept on 2D planar geometry, and the band gap was studied. The simulation results show that the band gap is very easy to be tuned by Cr doped BN sheet, which is more stable structure. So Cr doped BN sheet is a promising material in modulating the band gap and through tuning the band gap it can be a highly efficient photocatalytic material et al. Because Cr is poisonous and harmful substance, it does harm to people’s health and environmental pollution, particularly, heavy metal contamination in soil. So Cr doped BN sheet is a promising material in modulating the band gap, through tuning the band gap it can be a highly efficient photocatalytic material and benefit humanity and protect the environment et al.