Semiconductor nanocrystals (NCs) have received much interest for their optical and electronic properties. When these NCs dispersed in polymer matrix, brightness of the light emission is enhanced due to their quantum dot size. Silver doped cadmium sulphide NCs were synthesized through chemical route method with an average size of 5-8nm range. The impurity of Ag in CdS (CdAgS) is responsible for the additional defects which may tune the optical and structural properties in comparison to the pure CdS NCs. The synthesized NCs are characterized by XRD, XRF, SEM, and TEM. The effect of Ag doping and Swift heavy ion irradiation on optical properties of nanocomposite films is analysed by PL and UV measurements. The XRD results show that Ag doped CdS was grown in the hexagonal phase of about 10nm size as calculated by Scherer formula, which have good agreement with TEM measurements. The presence of silver in CdS nanoparticles is characterized by X-Ray fluorescence. These NCs were dispersed in PMMA matrix by solution cast method and irradiated by swift heavy ion (SHI) (100MeV, Ni⁺⁷ ion beam). The UV-Vis measurement show a red shift in optical absorption and band gap decreases after irradiation with respect to pristine CdAgS nanocomposite polymer film. Photoluminescence shows the enhancement in luminescence intensity after irradiation.