Silicon-doped diamond-like carbon (Si-DLC) film is of significant interest for tribological effects, because it has a very low friction coefficient and possesses the potential to improve wear performance in humid atmospheres and at high temperatures. Many experimental results of the Si-DLC film show that its tribological property changes greatly with silicon content. In this paper, we use molecular dynamics (MD) simulation to study sliding friction processes between DLC and Si-DLC films under dry friction and oil-lubricated conditions separately. The results show that after sliding, a transfer film between the DLC and Si-DLC films is formed under the dry friction condition. In contrast, a boundary lubrication layer is found under the oil-lubricated condition. Therefore the friction forces on the dry friction condition are larger than those on the oil-lubricated condition. Small addition of silicon atoms can reduce the friction force of DLC films indeed, but it has little effect to the friction force when the silicon content is larger than 20%. There is a obvious effect of the silicon content on the bond number of transfer films under the dry friction condition, and CC bond and CSi bond both first increase and then decrease, there is almost no little CSi bond at the end of the sliding.