Borophosphates,particularly BPO4(BPO)[1,2] crystals,have attracted attention in laser frequency conversion devices due to short ultraviolet cut-off edge and relatively large second harmonic generation(SHG) response with magnitude almost twice that of KH2PO4.Yet the birefringence of BPO(approximately 0.005) is too small to satisfy the phase matching condition[3] in ultraviolet spectral region,restricting the efficiency of laser output.Here we systematically examine the influence of mechanical strains on the atomic structure as well as the electronic and optical properties of BPO by the first-principles calculations applied in the CASTEP package of Materials studio.Interestingly,we find that the birefringence of BPO can be enhanced by～0.06 through the external uniaxial strain along c-axis.Meanwhile,the compressive strain can effectively increase the band gap and SHG coefficients.The refractive-index dispersion is also emphasized in this work.Our results indicate that phase matching in ultraviolet region(266 nm) could be achieved under-10 ％strain(3.9 GPa).This investigation is not only helpful for better understanding the structure-property relationship of BPO under strain,but also presents the possibility of its use as a promising ultraviolet nonlinear optical crystal.