Abstract: The a-C：H thin films were successfully fabricated on Si(111) substrates by plasma enhanced chemical vapor deposition (PECVD). The surface morphology of thin films was studied by atomic force microscopy (AFM) and scanning electron microscope (SEM). From the perspective of dynamic scaling, the evolution mechanism of the surface roughness for the a-C：H thin films was investigated. The results show that the surface morphology of a-C：H thin films is according to a kind of self affine fractal surface, and the surface roughness of thin films can be described by the fractal dimension. With the increasing of the flow of H₂, the surface roughness decreases firstly and then increases. When the flow ratio of T₂B and H₂ is 0.2/6, the surface roughness reaches the minimum of 2.2 nm, and the surface grain is in uniform and regular arrangement without crack.