In this study, we investigated the effect of nickel thickness on the structure and field-emission properties of carbon nanotubes (CNTs) films grown by microwave heating chemical vapor deposition. We found that the diameter, length, and field emission of CNTs films are strongly related to the nickel thickness in the range of 5-100 nm; i.e. these properties increase with the increasing nickel thickness. Specifically, the CNTs film grown on 100-nm-thick Ni exhibits the best microstructure and filed emission: a high aspect ratio of >34, a low turn-on field (~0.11V/μm), and a current density of 2.26 mA/cm2 when the electric filed is 5 V/μm.