Optical emission spectroscopy and Fourier transform power and impedance analysis have been used to investigate the effects of substrate bias and glow discharge on the plasma optical and electrical properties for the deposition of microcrystalline silicon. Results show that the Hα emission intensity distribution has the same tendency under bias AC，floating and -DC +AC, and their mean sheath lengths are almost located at the same position of the electrode gap. Compared to the above three bias states，Hα emission intensity increases sharply and double layers appear under +DC+AC bias and grounded conditions. Increasing of glow discharge power leads to the rise of Hα emission intensity，both the resistance and reactance decrease，and the plasma becomes more capacitive.