This study investigated the use of quadrupole mass spectrometer (QMS), optical emission spectrometer (OES) and Langmuir probe to diagnose the H 2-Ar-SiH4 plasma characteristics in cyclotron resonance chemical vapor deposition (ECR-CVD) process. The plasma physical characteristics such as electron density (Ne), electron temperature (Te), plasma and floating potential were obtained by Langmuir probe. The QMS and OES were used to identify the radicals in the plasma. Furthermore, the relative concentration and consumption of SiH4 in ECR-CVD process could be estimated by the TIMS (threshold ionization mass spectrometry) method based on the QMS results. The relationship between the film and plasma characteristics with varying process parameters was also discussed. As results shown, besides the degree of ionization, the consumption of SiH4 and the sheath potential (Vs) were key factors to affect thin film deposition rate (DR). When microwave power density rose from 1 w/cm2 to 3w/cm2, the DR has increased 194%, and it was nearly equal to the product of 104% in SiH4 consumption and 187% in Vs increase. The high hydrogen dilution ratio (H2/SiH4) would lead to higher electron temperature, density and Vs, but decrease the SiH4 consumption and DR. Moreover, the declining extent of DR was significantly greater than SiH4 consumption and Vs increase. It seems that the effect of hydrogen etching plays an important role due to the increase of high hydrogen dilution ratio (H 2/SiH4), This interpretation can be received from supporting evidence in OES measurements.