A novel coupled quantum well structure --- quasi-symmetric coupled quantum well (QSCQW) is proposed. In the case of low applied electric field (F = 25 kV/cm) and low absorption loss (α ~ 100 cm^(-1)), a large field-induced refractive index change (for TE mode, Δn = 0.0106; for TM mode, Δn = 0.0115) is obtained in QSCQW structure at operating wavelength λ = 1550 nm. The value is larger by over one to two order of magnitude compared to that in a rectangular quantum well (RQW) and about 50% larger than that of five-step asymmetric coupled quantum well (FACQW) structure under the above work conditions.