In this paper,we study the optical constants of hydrogenated microcrys talline silicon germanium alloy (μc-Si1－xGex:H) fabricated by plasma enhanced chemical vapor deposition (PECVD).First we propose a Matlab method to a bstract optical constants from the transmission spectra,which is based on multi -layer model and the Cauchy dispersion formula. Compared with traditional fringe pattern methods,such as Swanepeol method,pointw ise unconstrained minimization approach (PUMA),the Matlab method determines the refractive index not from the amplitude of the interference fringe but from the position of the interference fringe,so it can avoid the negative i nfluence owing to the deviation of the amplitude and can offer more precise optical constants,and it can enhance the fitti ng precision by one order of magnitude.The results show that the absorption coefficients and the refractive indices of μc -Si1－xGex:H are higher than those of μc-Si:H in the whole spectrum,and increase as the Ge content increases.The further results cal culated by advanced semiconductor analysis (ASA) demonstrate that compared with μc-Si:H,μc-Si1－x Gex:H PIN solar cells with the same thickn ess present higher quantum efficiency (QE) response from 400nm when the absorber is thin,and can also achieve higher QE response in the near-infrared region when the absorber is thick.On the other hand,to realize the same current density,μc-Si1－xGex:H can reduce the thickness effectively,so it can reduce the fabricating cost of thin film solar cells apparently.