The unusual strip-shaped diamond crystals were successfully synthesized in the Fe3Ni3C systems with h-BN additive. Our results showed that the morphology and color of our obtained diamond changed significantly compared with the diamond that synthesized by using conventional catalysts, which was attributed to the presence of h-BN additive. The incorporation of B and N atoms into the diamond structure played an important role in the formation of strip-shaped diamonds. The complex bonds environment of the boron/nitrogen co-doped strip-shaped diamonds should be more attractive in future study on the new behaviors for electronic and optoelectronic devices. The simultaneous incorporation of boron and nitrogen could tend to enhance the quality of strip-shaped diamonds. This work would provide a new synthesis technique to enrich the shape of the diamond crystals and stimulated future experimental exploration for industrial needs.