The work aims to investigate the effects of silicon (Si) and oxygen (O) element doping on the deposition, structure, surface morphology, and barrier properties of diamond like carbon (DLC) films, providing new ideas and references for the efficient preparation of high barrier Si and O co-doped DLC (Si/O-DLC) films. Microwave plasma enhanced chemical vapor deposition (PECVD) technology was used to deposit Si/O-DLC films on the surface of polyethylene terephthalate (PET) substrate, the effect of hexamethyldisiloxane (HMDSO) content in the reaction monomer on film deposition and properties was specifically studied. The thickness, structure, and microstructure of the composite film were characterized by profiler, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM), and the barrier properties of the composite film was characterized by testing the oxygen permeability. As the content of HMDSO in the mixed gas increased, the deposition rate of the film increased, and the fluctuations in the deposition rate at different height positions weakened, with an average deposition rate of up to 310 nm.min-1. At the same time, the content of Si and O elements in the film increased, the content of related bonding structures rose, the surface density of the film deteriorated, and the oxygen barrier properties weakened. When the HMDSO flow rate was controlled at 1mL.min–1, the oxygen permeability of PET film could be reduced from 132 mL.m2.d–1 without coating to 2 mL.m2.d–1, and the barrier properties were significantly improved. Under certain working conditions, coating Si/O-DLC film on the surface of PET film with microwave PECVD technology can significantly improve its barrier properties.