To solve the problem of interfacial bonding strength between diamond-like carbon （DLC） films and metal substrates， this study uses direct current plasma enhanced chemical vapor deposition （DC-PECVD） technology to deposit composite DLC films under the same duration but with different negative bias voltage conditions on 45 steel substrates. A scanning electron microscope （SEM） and an atomic force microscope （AFM） were used to observe the morphology of the films， a Raman spectrometer was used to analyze their compositions， and a coating adhesion automatic scratch tester was used to determine the bonding strength between the films and substrates. The results show that when the bias voltage changes from -600 V to -1 200 V， the surface roughness of the films increases， the total film thickness increases （up to 16.3 μm）， the hydrogen content decreases， the graphite relative content increases， and the structural composition difference between the transition layer DLC and the top DLC film decreases. Meanwhile， the residual stress increases， the binding force decreases， and the maximum value is approximately 54.5 N. When the bias voltage of the top DLC layer is between -600 V and -800 V， the comprehensive performance improves.