In deposition of the diamond-like films by electron assisted plasma chemical vapor deposition, two systems (CH4/H2 and CH4/H2/Ar) have been used and compared. The electron temperature and electron density have been measured by means of Langmuir single probe. The results show that the electron density in CH4/H2/Ar is higher than that in CH4/H2, and the growth rate of the films increases in CH4/H2/Ar system.