The studies on model systems XAuPH3 (X=H, F, Cl, Br, I, CN, CH3 ) have been carried out by using ab intio HF and DFT B3LYP methods at pseudopotential and dou-ble-zeta LANL2DZ level. The results are compared with those of MP2. The properties of the models, i.e. the atomic net charge populations, the frontier molecular orbitals and nonlinear optical (NLO) properties have been investigated under an applied electric field on the basis of optimized structures. The computational results show that for these models characterized as electron acceptor-metal-electron donor (A-M-D) system, the NLO properties are due to in-tramolecular charge-transfer interaction between the accep-tor and the donor. The more charges transfer gives, the bet-ter NLO properties. In the selected model systems, IAuPH3 has the biggest bvec and g of 1184.1942 a.u. and 17341.9214 a.u., whereas IC6H4PH3+, a typical A--D organic conjugated system, has bvec and of 710.7697 and 11664.1405 a.u. respec-tively. In comparison, IAuPH3 has significant NLO proper-ties. The studies on model systems XAuPH3 (X = H, F, Cl, Br, I, CN, CH3) have been carried out by using ab intio HF and DFT B3LYP methods at pseudopotential and dou-ble-zeta LANL2DZ level. The results are compared with those of MP2. The properties of the models, ie the atomic net charge populations, the frontier molecular orbitals and nonlinear optical (NLO) properties have been investigated under an applied electric field on the basis of optimized structures. The computational results show that for these models characterized as electron acceptor-metal-electron donor (AMD) system, the NLO properties are due to in-tramolecular charge-transfer interaction between the accep- tor and the donor. The more charges transfer gives, the bet-ter NLO In the selected model systems, IAuPH3 has the biggest bvec and g of 1184.1942 au and 17341.9214 au, while IC6H4PH3 +, a typical A - D organic conjugated system, has bvec and of 710.7697 and 11664.1405 au respec- tively. IA uPH3 has significant NLO proper-ties.