Boron doped diamond thin films have been widely used in the electrochemical sensing applications for its outstanding electrochemical properties. In this work, the preferred (100) growth orientation of boron doped diamond films was successfully synthesized by applying different boron/carbon (B/C) concentration ratio in a homemade microwave plasma enhanced chemical vapor deposition system and its formation mechanisms was further studied. Moreover, the influences from substrate temperature and carbon source concentration were also debated to achieve better (100)-oriented diamond. The experimental results showed that B/C concentration ratio played a more important role on diamond morphology compared with substrate temperature and carbon sourceconcentration. While the B/C concentration ratio was constant with 4 000 ppm, crystal edges and face of the tetrahedral diamond particles became smoother and flatter, which indicated quality improvement of the obtained diamond particles. Keeping the B/C concentration constant, the secondary diamond nucleation density was enhanced when the temperature and carbon source concentration were increased. The results show that the highly oriented diamond thin film electrodes could be obtained by applying appropriate B/C concentration ratios.