A new lead(Ⅱ)borate,(Pb4O)Pb2B6O14,has been synthesized by low-temperature hydrothermal method.It crystallizes in the noncentrosymmetric polar space group P1 and structurally features a three-dimensional framework composed of paralleled spiral B6O14 chains connected by the Pb cations and isolated oxygen-centered Pb4O tetrahedra.It exhibits a phase-matching powder second harmonic generation(SHG)effect of about 3.5 times that of KH2PO4(KDP)at the 1064 nm fundamental wavelength.It also has optical band gap of 3.3 eV and high thermal stability up to 480 ℃,which make it a promising candidate for nonlinear optical(NLO)material.In addition,electronic structure and NLO property are studied by the first-principles method,and the calculated NLO coefficients are consistent with the experimental observations.The important contributions of Pb4O tetrahedra and the borate groups to the SHG response have been identified by the SHG-density method.