The synergetic lubrication effects between amorphous carbon (a-C) films and lubricating oils have drawn much attention for the past decades, and related researches suggest that the molecular structure and physicochemical properties of base oil could strongly affect the tribological behavior of a-C films. Here, we report a unique tribological behavior of nonhydrogenated a-C film when slides against the steel counter-parts in polydimethylsiloxane (PDMS), where the a-C film is severely fractured at the onset of sliding, but achieves a very low steady friction coefficient which is only about 50% of the one obtained in the poly-alpha-olefin (PAO). Via detailed morphological, chemical analysis and designed verification experiment, it is proposed that the initial high adhesion between a-C and steel in PDMS accounts for the fracture failure of the analyzed a-C film, while the chemical adsorption of decomposed PDMS on a-C surface is responsible for the reduced friction. Finally, we present an effective method to eliminate the cracking behavior while retain the low friction performance for steel/a-C contacts in PDMS.