A field-induced electron emission phenomenon has been observed from nitrogen-doped diamond films deposited on molybdenum substrates by microwave plasma enhanced chemical vapor deposition using N2 /CH4 as feedstock. Their field-induced electron emission characteristics, i.e., current-voltage characteristics and distribution of emission sites, were studied using the transparent anode imaging technique. A repeatable abrupt change of "on" and "off" states of emission was observed at two corresponding specific fields during circling of both increasing and decreasing applied gap fields. A plausible explanation is given to this type of field-induced electron emission phenomenon, in which a two-layer structure consisting of amorphous carbon and diamond is proposed.