ZnSe:Co　thin　films　were　grown　on　quartz　substrates　at　various　ambient　pressure　by　pulsed　laser　deposition.　The　propagation　of　plasma　plume,　the　structure　and　optical　properties　of　films　at　pressure　of　1Pa　to　10Pa　had　been　investigated.　With　the　ambient　pressure　increased,　the　angle　of　divergence　and　propagation　distance　of　plasma　plume　changed,　the　crystal　structure　of　films　investigated　by　XRD　showed　that　the　crystal　quality　of　films　was　promoted.　The　optical　band　gap　and　refractive　index　were　analyzed　by　the　transmission　spectra.　The　optical　band　gap　first　decrease　then　increase　with　increasing　deposition　pressure,　which　may　be　associated　with　the　quantum　confinement　effect.　The　refractive　index　increased　with　increasing　deposition　pressure,　which　may　be　due　to　the　promotion　of　the　film　density.　The　dispersion　parameters,　E-0,　E-d,　the　static　refract　ive　index　(n(0))　and　static　dielectric　constant　(e(0))　were　calculated　according　to　the　single　oscillator　model.