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Nitrogen doped diamonds with great application potentials can be synthesized by using different doping sources (i.e., urea and N2), effects of which on growth behavior and properties of diamond films on WC-Co substrates were presented in this paper. The doping efficiency of urea was always higher than 0.12, much higher than that of N2 (always lower than 0.04). The sufficient N2 addition could increase growth rate, and induce apparent grain nanocrystallization, by modifying reactant gas phase chemistry. The grain nanocrystallization contributed more to the reduction of the surface roughness, and degradation of the diamond purity and mechanical properties. On the contrary, the urea doping resulted in much less degradation of the diamond purity and mechanical properties, while providing sufficient N incorporations into the diamonds. Besides, urea doping promoted the formation of the diamond (220) planes on the polycrystalline diamond surfaces, which had a close relationship with the actual N doping concentration in the diamond. The controllable adjustment of the growth and properties of diamond films, by selecting the doping source and optimizing the doping ratio, could help to meet distinctive application requirements, and balance the machining efficiency and application performance of diamond coated components.