Abstract: Aim To study carbon state in detonation process of high density negative oxygen balance explosives.Methods\ Based on numerical modeling of detonation synthesis of ultrafine diamond (UFD) and experimental study of solid detonation products, the state of free carbon was discussed. By using the equations of states of pure graphite, diamond, ultrafine diamond and liquid like carbon, the detonation velocities of some explosives were calculated.Results and Conclusion Equations of states of ultrafine diamond and liquid like carbon can give better predictions to the detonation parameter of explosives than that of pure graphite and diamond. It demonstrates, for high density explosives, at CJ point in detonation, free carbon is more likely in the state of liquid carbon or liquid like carbon.