Abstract: To study the changes of forzen storage time on protein properties of pork longissimus dorsi,the gel electrophoresis and differential scanning calorimetry were used to analyze the hydrophobicity,sulfhydryl content,degradation and thermostability of pork longissimus dorsi after frozen storage at -18 ℃ for 0 day and 1,3,6,9,12 and 15 months. The results showed that with the prolonged storage time,the protein solubility decreased significantly(p<0.05),the hydrophobicity and sulfhydryl content of myofibrillar protein(MPI)increased,the MPI degraded was mainly located near 67 kDa and 20~29 kDa. The denaturation temperature and denaturation enthalpy of myosin and sarcoplasmic protein showed a decreasing trend. This showed that the thermal stability of these two types of proteins was reduced. In the first 3 months,the indicators remained at a good level,but after 6 months during the frozen storage,the change amplitude and rate of all indicators increased rapidly. These showed that after 6 months frozen storage,the protein quality of pork longissimus dorsi began to decrease rapidly.