Carbon nanotubes (CNTs) have been grown efficiently on a Si substrate by thermal chemical vapor deposition using CH4 and CO2 gas mixtures. Fe catalytic nanoparticles were deposited on Si and carbon cloth substrates. This process is apparently different from the conventional process in gas mixtures of H2/CH4, H2/C2H2, NH3/CH4, H2/C6H6 and others. Carbon dioxide is used to replace the harmful gases of H2 and NH3 and the addition of N2 in the mixture gas of CH4 and CO2 obviously improves the growth and quality of CNTs, and allows study of the reaction growth of CNTs. This paper demonstrates the effects of compositional ratio of CH4, CO2 and N2 in the mixture gas on the growth of carbon nanotubes under atmospheric conditions. Various substrates of Si and carbon cloth were used to synthesize CNTs by using CH4-CO2-N2 gas sources. A significant difference in morphological structure was observed and analyzed on the different substrates of Si and carbon cloth. By proper adjustment of growth parameters, high quality CNTs were observed on Fe-deposited substrates. The characteristics of the as-grown carbon nanotubes on different substrates were analyzed by SEM, TEM and Raman spectroscopy.