The optical property of amorphous fluorinated carbon (α-C∶F) films are investigated, which are prepared by microwave electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) using trifluromethane (CHF3) and benzene (C6H6) as source gases. The optical energy gap Eg of the α-C∶F films deposited at 140—700W powers and CHF3∶C6H6=1∶1—10∶1 are between 1.76 and 2.85eV. The amount of fluorine in the films has an effect on optical absorption and energy gap. The absorption edge increases as the amount of fluorine is raised. The optical energy gap Eg is mainly determined by CF bond in the films, which results in the change of the density of states in band tail of the valence band.