The first metal nitrate fluoride nonlinear optical material, Pb2(NO3)2(H2O)F2, was synthesized with the largest second harmonic generation (SHG) effect (12 × KH2PO4) among nitrates. Theoretical calculations revealed the synergistic effect of [NO3]-, lone pair electrons in Pb2+, and F- for the SHG effect. The F- also promoted the blue-shift of the ultraviolet cut-off edge.