Abstract: The field emission characteristics of the amorphous diamond films (a-DF) deposited by FAD (Filtered vacuum Arc Deposition) on silicon substrate at different bias voltage was studied and the electron emission characteristics of three kinds of a-DF with different proportion between sp³ and sp₂ bonds were compared. A series of bias experiments and life tests were carried out and the observed results were analyzed. Based on that, a field emission mechanism of the a-DF was suggested.