Abstract: The bias-enhanced nucleation of diamond on mirrorpolish Si(100) has been studied by using orthogonal method in a microwave plasma chemical vapor deposition (MPCVD) reactor. The effects of process parameters such as bias voltage, methane content, bias time and gas pressure on diamond nucleation are investigated. The results show that the diamond nucleation density increases in direct ratio with the nucleation time. The moderate bias voltage and gas pressure are beneficial to diamond nucleation while the effect of the methane concentration on the nucleation is negligible. The optimum nucleation condition obtained from orthogonal test is bias voltage -250V, nucleation time 12min, gas pressure 4kPa and methane concentration 4% under which a very high nucleation density up to 10¹⁰/cm² has been achieved.