Bromine doped hydrogenated amorphous carbon(a-C∶Br∶H)thin films were deposited on silicon wafers by rf. -plasma enhanced chemical vapor deposition(RF-PECVD) with a frequency of 13.56 MHz at room temperature using pure bromoethane as a precursor of carbon source mixed with hydrogen(H₂) as a carrier gas. The structures of the films prepared by partial pressure of mixed gas(C₂H₅Br/H₂)were studied by Raman spectroscopy. The results indicate that the intensity of the Raman D peak is stronger, the Raman G peak positions shift up a little, and the value of I_D/I_G increases from 1.18 to 1.36, if the gas pressure of mixed C₂H₅Br/H₂is reduced gradually from 20 to 5 Pa. Meanwhile, the growth of thin film turns gradually into low energy mode promoting the transform of sp²-C from chains to rings.