The study of field emission property on nitrogen doped tetrahedral amorphous carbon (ta-C:N) prepared by filtered cathodic vacuum are, (FCVA) technique is reported. Field emission from ta-C:N coated on Si substrate was investigated by ''plane-to-plane'' configuration at room temperature and base pressure of 2.0x10(-6) torr. A comparison of the field emission characteristics for various nitrogen flow rate showed significant shifts in J-E curves towards low potential side with the increasing of nitrogen flow rate. The lowest onset field obtained was 10V/mu m. The current density of 0.1 mAmm(-2) (assuming the entire plm surface is emitting) at 50V mu m(-1) was obtained from these film. Electronic parameters, i.e., band gap energy and activation energy were measured in order to construct a energy band diagram for the heterojunction structure and the field emission mechanism is proposed based on this structure.