Thanks to the unique properties, nanocrystalline-diamond is a valuable material that is widely used in nano-electronic device fabrication to enable the new promising power device applications in the near future. In general, the hydrogenated-(C-H) nano-diamond metal oxide semiconductor (MOSFET) depicts the normally- on status (depletion mode). In this paper, to confirm normally-on operation and show the characterization of normally-off operations with a controlled gate of the power device and study the corresponding impact, we simulate the two-dimensional (2D) C-H nano-diamond MOSFET under several surface charge models' impact. The enhancement mode, called normally-off, is attained to realize a safety point of the power device. The results also show the shifting tendency of the threshold voltage to a negative value with a positive charge model, given that, in principle, this state is impractical without a donor doping or oxidation layer.