A dielectric/metal/dielectric (D/M/D) film with a high visible (0.38-0.78 mu m) transmittance and a high solar infrared (0.78-2.5 mu m) reflectance can be applied on the outdoor surface of a window for energy saving in hot weather. However, in this kind of application with a D/M/D film, the regulation of long-wave ( > 3 mu m) radiation is often neglected but proved to be significant in energy saving according to our previous work. For a ZnO/Ag/ZnO structure on flexible PET applied as a visible transparent solar infrared reflecting film with a low long-wave emittance, based on matrix formulation and a ray-tracing method, the influence of Ag layer thickness on visible transmittance (T-vis), solar infrared reflectance (R-si) and long-wave emittance (epsilon(lw)) are investigated. Two samples with the highest T-vis, and Tvis + R-si are prepared, respectively, with high visible transmittance, high solar infrared reflectance and low long-wave emittance, simultaneously. In hot weather, compared with a traditional silica glass, the exterior applied film consumes more energy, while the interior applied film saves 9.6% energy consumption for cooling.