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We propose a novel coupled quantum well structure, i.e. a quasi-symmetric coupled quantum well (QSCQW).Based on the demands of optical switching devices for quantum well materials, the QSCQW configuration isfurther optimized. Consequently, in the case of low applied electric field 25kV/cm and low absorption loss100cm-1, a large field-induced refractive index change (for TE mode, n = 0.0106; for TM mode, n = 0.0115)is obtained in the QSCQW structure at the operation wavelength 1550nm. The value is in one or two order of magnitude larger than that in a rectangular quantum well and about 50% larger than that of five-step asymmetric coupled quantum well structure under the same working conditions. The refractive index change obtained with the optimized QSCQW under so low absorption loss and applied electric field is very attractive for semiconductor optical switching devices. This manifests that the QSCQW structure has a great potential for applications in ultra-fast and low-voltage optical switches and in travelling wave modulators.