Abstract: The polystyrene was filled and modified with rutile nano-TiO₂ as antiaging additives.It was noted that low molecule organic substance was ingrafted onto nano-TiO₂ after surface modification,consequently which upgrading its consistent and disperse property in HIPS resin.After 28 days exposed to xenon arc lamp,the mechanics of HIPS modified by nano-TiO₂ kept for a long time.Furthermore,the ability of resisting color aberration was improved,and that rupture of molecule chain was restrained effectively.According to FTIR analysis,the aging mechanism revealed that the cooperating effect of nano-TiO₂ in company with organic UV-absorbent could restrict aging rate of modified HIPS in effect.Moreover there was little change for absorbing characteristic of carbonyl and hydroxyl group in the 28 days accelerating aging period.