Structural properties of microcrystalline silicon films deposited by very high f requency plasma_enhanced chemical vapor deposition(VHF_PECVD) and on-line monit or were studied using Raman and optical emission spectroscopy. The results obta ined showed that the discharge power has a modulation function on crystalline volume fraction (χc) of materials. A larger silane concentration means a stronger modulation function. The intensity of SiH* peak can characterize the deposition rate in a certain range, however the higher power indicates the lower deposition rate, and the ratio of intensity Hα* to SiH* peak value reflects the extent of crystallinity which is consistent with the result obtained from Raman measurement. In addition, the ratio of I［Hβ *］／ I［Hα*］ indicates the decrease of electronic temperatur e in hydrogen plasma with the increase of discharge power.