Abstract: In order to evaluate the freshness of chilled mutton, a time-temperature indicator ( TTI) system based on lipase was investigated in this paper.The optimal ratio of the mixed indicator was 2∶3∶10 due to Cresol red, Bromo phenol blue musk and Phenolphthalein.TheTTI system was established as Gly-NaOH buffer solution ( 39.5mL, pH9.00) , Polyvinyl-tributyrin ( 7.5mL) , 2.0g·L- 1 ( 1.0mL) lipase, mixed indicator ( 1.0mL) , 1mol·L- 1Ca2 +solution ( 1.0mL) where lipase served as substrate. In the same condition, the volatile basic nitrogen ( TVBN) value was also determined and the color of the reaction system was associated with the freshness of mutton directly.