The work aims to improve field emission properties of carbon films. By taking advantage of hot filament chemical vapor deposition (HFCVD) technology, carbon films with different microstructures were prepared by applying external fields (electric field, magnetic field and electromagnetic coupling field)in respect of different methane concentrations 1% and 5% (volume fraction, full text of the same ). Surface morphology of the films was observed using SEM, composition of the films was detected using Raman, andfield emission properties were characterized using field emission testing device. As a means of innovating traditional crafts, external field could influence the deposition process of CVD. The magnetic field could reduce grain size while electric field could effectively promotetranformation from sp3 phase to sp2 phase. On this basis, electromagnetic coupling field could effectively control surface morphology of high aspect ratio. Diamond film was prepared and turn-on field was 11.2 V/μm provided with methane concentration of 1%. After electric field or electromagnetic coupling field was applied, the film surface was etched, the diamond film was transformed into graphite film, turn-on field was reduced to 6.75 V/μm and the field emission properties were improved. Provided with methane concentration of 5%, turn-on field of the film prepared by magnetic field or electric field was reduced from 12.75 V/μm to 11.5 V/μm and 9 V/μm, respectively, sharp-pointed morphology, high content of graphite phase, lowest turn-on field (5.65 V/μm) the best field emission properties could be obtained provided with etching effects of electromagnetic coupling field. Various films can be prepared in the mode of external field (electric field, magnetic field and electromagnetic coupling field)-assisted HFCVD. The electromagnetic coupling field at high concentration of methanecan not only improve content of graphite phase, but also obtain the surface morphology of high aspect ratio, and therefore effectively improve the field emission properties of films.