The first hyperpolarizability of two tungsten-carbonyl complexes, tungsten pentacarbonyl pyridine and tungsten pentacarbonyl trans-1,2-bis(4-pyridyl)-ethylene, has been studied by the high-level TDDFT method. The consideration of the solvent effect and intermolecular pi-pi weak interaction in the calculations quantitatively improve the final result of both the electronic excitations and the first hyperpolarizabilities. By using the orbital decomposition scheme (J. Phys. Chem. A 2006, 110, 1014-1021), the NLO mechanisms of these two complexes have been ascribed to the dominant contribution from the metal-to-ligand charge transfer, with HOMO -> LUMO character, and the indispensable contribution from the intraligand charge transfer as well. A supplementary formula has been proposed to implement the orbital-pair transition analysis. This study reports the significant influences of solvation and intermolecular interactions on the first hyperpolarizabilities of organometallic NLO chromophores.