H2 and He gas mixture diluted very high frequency plasma assisted reactive thermal chemical vapor deposition (VHFPA-RTCVD) is used to prepare μc-SiGe:H thin films, and the optical emission spectrum is used to in situ monitor the reacting plasma during the growing process. It is observed that H2 and He gas mixture dilution is effective in increasing the number of Hα* and reducing the temperature of electrons in the plasma. X-ray diffraction (XRD) and photo- and dark-conductivity measurement show that by optimizing the fractions of H2 and He in the mixture the defect states are reduced, which prompted the growth of and improved the structure, and the optical-electronical properties of the film are enhanced.