Abstract: The accelerated aging experiments for PMMA specimens have been conducted for 70 days under the conditions of ultraviolet air (50℃ temperature, 313nm wavelength), and macro-mechanical characteristics of PMMA were tested at different time during the experiments, and structure difference were analyzed between samples before aging and after aging by methods of GPC and DSC. Combined with the mechanical data, the aging rule and aging mechanisms for PMMA in ultraviolet were clarified qualitatively.