In this work, based on bis(tetrathiafulvalenyldithio)-germane (bis-TTF-Ge), 37 compounds (noted T0-T36) are designed by introduction of donor and acceptor groups at different substituent positions. The ground state electronic structures, reactivity indices, electronic transition, charge transfer properties (charge, distance and dipole moment), hyper-Rayleigh scattering and depolarization ratios (static and dynamic) of these compounds are fully investigated by DFT and TD-DFT theory. The quantum calculations were performed at the CAM-B3LYP/6-311g(d,p) level and the sum-over-states (SOS) approach in both static and dynamic cases. The chemical hardness (η) of the two substituted bis-TTF-Ge at the b position has a smaller value than those with the same substituent at positions d, e, a and c. In both static and dynamic regimes the investigations show that the bis-TTF-Ge substituted with donor or acceptor groups have larger first hyperpolarizability than T0. Our work predicts that the introduction of the substituent group at the b position can increase the hyperpolarizability values more than at the other positions, and the NO2, NO and COCN acceptor groups, lead to the largest values. For example, the dynamic β_HRS^(=1064) value of T25 is about 145 times larger than that of T0 and about 11 times than that in the static regime. Interestingly, the β_HRS^(=1064) of bis-TTF-Ge substituted with NO2 group increases with the number of NO2 in the TTF fragment. The large nonlinear optical (NLO) origin of bis-TTF-Ge substituted with NO2, NO and COCN is attributed to charge transfer from the TTF to the acceptor group at the second TTF fragment. The studied bis-TTF-Ge substituted with NO2 compounds exhibit the possibility to be excellent second-order NLO materials.