The tendency of graphite-diamond transformation assisted by nonmetallic catalysts of carbonates, sulfates, or phosphorus under high pressure and high temperature has been investigated by calculating the activation energy and transformation probability of the carbon atoms over a potential barrier. It was found that the activation energy is highly sensitive to the catalyst chosen. The value of activation energy in the systems of graphite-carbonates, graphite-phosphorus, and graphite-sulfate are 130.71 × 103, 206.03 × 103, and 221 × 103 J/mol, respectively. If fd stands for the probability of the transformation from graphite to diamond, the probability sequence of graphite-diamond transformation in different systems was put forward: fd(gr.-carbonate) > fd(gr.-phosphorus). fd(gr.-sulfate).