Phosphates　are　ideal　candidates　in　the　search　for　deep　ultraviolet　(DUV)　nonlinear　optical　(NLO)　materials　due　to　their　wide　DUV　transmission.　However,　the　small　optical　anisotropy　of　the　highly　symmetric　[PO4](3-)　tetrahedron　hinders　phase　matching　(PM)　in　the　DUV　wavelength　range.　In　this　work,　the　polar　tetrahedron　[PO2(NHCONH2)(2)](-),　which　combines　the　pi-conjugated　urea　unit　and　the　non-pi-conjugated　[PO4](3-)　unit　via　covalent　bonds,　is　proposed　as　a　new　DUV　NLO-active　unit.　[PO2(NHCONH2)(2)](-)　tetrahedron　exhibits　greatly　improved　polarizability,　anisotropy,　and　hyperpolarizability　while　maintaining　a　large　highest　occupied　molecular　orbital-lowest　unoccupied　molecular　orbital　gap.　Accordingly,　two　DUV　transparent　alkali　metal　N,　N-bis(aminocarbonyl)-phosphorodiamidates　[A[PO2(NHCONH2)(2)]　(A　=　K,　Rb)]　are　screened　out,　and　their　nonlinear　properties　are　systematically　evaluated　by　first-principles　methods.　The　results　show　that　K[PO2(NHCONH2)(2)]　(KPOU)　achieves　significant　enhancements　in　multiple　properties　compared　to　the　existing　phosphate　DUV　NLO　materials,　including　a　strong　SHG　effect　(3.44　x　KDP)　and　the　largest　birefringence　(0.088@532　nm)　for　DUV　PM.　Moreover,　the　shortest　PM　wavelength　(lambda(PM))　of　KPOU　is　196　nm,　making　it　a　promising　DUV　NLO　candidate　for　practical　applications.　This　work　proposes　an　excellent　NLO-active　unit　and　offers　a　new　direction　for　exploring　novel　high-performance　DUV　NLO　materials.