The effect of catalysts on carbon nanotube growth by microwave heating CVD is investigated. The catalysts used in this study were various concentrations of iron, cobalt, or nickel nitrates. Among these three catalysts, iron yields the best field-emission quality of carbon nanotube films. Moreover, the density of carbon nanotubes increases with increasing concentration of catalyst. For the film grown with a 2M ferric nitrate as catalyst, a maximum emission current density of 5mA/cm^2 with low turn-on field of ~1.059 V/μm can be achieved.