Diamond like carbon (DLC) films have been extensively studied over the past decades due to their unique combination of properties, in particular, silicon-doped DLC (Si-DLC) films are of significant interest for tribological effects, they had a very low friction coefficient and possess the potential to improve wear performance in humid atmospheres and at higher temperature. But many experimental results of the Si-DLC films showed that their tribological properties changed greatly on different silicon contents. In the paper, molecular dynamics (MD) simulations were used to study a sliding friction process between Si-DLC and DLC films on an un-lubricated and a water-lubricated condition respectively. The results have been shown that a transfer film between the Si-DLC and DLC films was formed on the un-lubricated condition. In contrast, a boundary lubrication layer was found on the water-lubricated condition. Moreover, the friction force on the un-lubricated condition was larger than those on the water-lubricated condition.