A new type of photodegradable poly(vinyl chloride)-bismuth oxyiodide/TiO2 (PVC-BiOI/TiO2) nanocomposite film was prepared by embedding a nano-TiO2 photocatalyst modified by BiOI into the commercial PVC plastic. The solid-phase photocatalytic degradation behavior of the as-prepared film was investigated in ambient air at room temperature under UV light irradiation, with the aid of UV-Vis spectroscopy, weight loss monitoring, scanning electron microscopy, and FT-IR spectroscopy. Compared to the PVC-TiO2 nanocomposite film, the PVC-BiOI nanocomposite film and the pure PVC film, the PVC-BiOI/TiO2 nanocomposite film exhibited a higher photocatalytic degradation activity. The optimal mass ratio of BiOI to TiO2 was found to be 0.75%. The weight loss rate of the PVC-BiOI/TiO2 nanocomposite film reached 30.8% after 336 h of irradiation, which is 1.5 times higher than that of the PVC-TiO2 nanocomposite film under identical conditions. The solid-phase photocatalytic degradation mechanism of the nanocomposite films was briefly discussed.