β-glucan/pectin composite films were prepared by mixing proper amounts of pectin and glycerin with β-glucan. The mechanical properties, barrier properties (against moisture and oxygen), thermal properties, film forming mechanisms, and water distributions of the composite films were compared using a texture analyzer (TA), a X-ray diffraction instrument (XRD), a scanning electron microscope (SEM), an infrared spectroscopy analyzer (FTIR), a differential scanning calorimeter (DSC), a nuclear magnetic resonance imaging analyzer (NMR) and a thermogravimetric analyzer (TGA). Moreover, the structure and properties of different β-glucan/pectin composite films were studied, and the optimal ratio of raw materials for composite film preparation was determined. The film obtained using 3:1 β-glucan-to-pectin mass ratio (film BP4) exhibits better mechanical properties and higher oxidation resistance due to the stronger interactions between β-glucan and pectin and denser film structures than those of films comprising the same materials at other proportions. Furthermore, β-glucan and pectin have good compatibility, and the thermal stability of the film is the best. The findings could provide reference for the rational application of polysaccharide composite films in food packaging.