We have fabricated p-type and n-type carbon nanotube transistors (CNTFETs) by using high and low work-function metals Pt and Al as contact electrodes， respectively. The band structures indicate that the work functions of contact metals play an important role in operation mechanism of CNTFETs. We can obtain fine-tuning of Schottky barrier heights for p- and n-channel conductions by changing the contact metals. These results can be explained by taking into account the work functions of the contact metals.