Amorphous carbon film is composed of sp2 bonding and sp3 bonding carbon atoms.The ratio of sp3/sp2 bonding carbon is an important parameter to determine the structure and properties of amorphous film.And the surface roughness of DLC thin film was one of important influencing factors to high quality optical thin films,especially,which used in high power laser syetem and gyro.In this paper,the surface roughness of DLC film and substrate were measured by TalySurf CCI non-contact roughness tester produced by United Kingdom Taylor-Hopson Co.,Ltd.Its the best vertical resolution is 0.1(A),test the range of 0.8mm × 0.8mm.The test results were obtained with the average of measured value of three points,and avoiding the more obvious flaws in the measurement process.The carbon bonding ratio in diamond-like carbon (DLC) thin films has been estimated from the ε2 spectra obtained by spectroscopic ellipsometry.This method has been used to find out the atomic fractions of sp3 and sp2 bonded carbon atoms by combining the various features of the existing methods.The atomic fraction of sp2 carbon atoms has been determined by fitting the gaussian curves in the experimentally observed ε2 spectra in the low energy range (< 4eV).The atomic fraction of sp3 bonded carbon atoms has been determined by calculating the total electron density in the DLC matrix.In this paper,DLC thin films were deposited by UBMS and PVAD.By changing the process parameters,the samples with different sp2 and sp3 bond ratio,different surface roughness were obtained.We have studied the correlation of the surface roughness and sp3/sp2 ratio.