Abstract: Nitrogendoped diamond films were synthesized by electron assisted chemical vapor deposition. The quality and chemical state of nitrogen in the diamond films were characterized by SEM, Raman, XPS, and EPR. Results showed that the morphologies of the diamond films changed from integrated facets to the “cauliflower-like” diamond (100) faces, the amorphous carbon content increased and its quality dropped with increasing nitrogen flow rate. The chemical state of nitrogen in the diamond films was of the form Ns0, N-V0 and N-V-1. The amounts of N-V0 and N-V-1 were higher when the nitrogen flow rate was lower, and the mass fraction of Ns0 varied from 1.50×10-5 to 4.83×10-4.