Diamond films with different boron concentrations are prepared by using microwave plasma chemical vapor deposition with ethanol-boron-oxide solution as boron source.SEM, XRD, Raman spectroscopy and electrochemical work station were used to observe and study the surface morphology, crystal structure and electro-chemical properties of the film.Resultsshow that with the increase of boron concentration, crystalline size of diamond film first decreases and then increases, while the potential window decreases from 3.1 V to 2.6 V and the anodic current decreases from 0.022 7mA·cm
-2 to 0.011 9 mA·cm
-2.But such increase has almost no influence on background current and electro-chemical reversibility.