In this paper, mass production of quasi-aligned CNTs was achieved with a new tri-metallic catalyst (Fe-Ni-Mo/MgO) by thermal CVD method, using methane as carbon precursor. The growth process was in-situ monitored by thermal gravimetry/differential scanning calorimetry (TG-DSC) technique, and the yield of CNTs over 2200% was attained under the mixture atmosphere of CH4 and H2 with flow rate about 25 ml/min and 5 ml/min respectively at 900°C for 30 min. The as-prepared products were characterized. Raman spectrums showed that the CNTs are multi-wall structure. The diameter of the CNTs was estimated to be 20-30 nm. We think the synergism of FeNi3 alloy and Mo is the main reason for the high catalytic activity of tri-metallic catalyst.