The application of wild trypsin is severely limited due to the antigenicity of heterologous protein, degradation by protease, low activity and poor stability. In order to obtain a trypsin with stable physical and chemical properties, the modification conditions of the trypsin by dextran and its enzymatic characteristics before and after modification were studied in this paper. The results showed that the optimal modification conditions of the trypsin by dextran were as follows: the molar ratio of dextran and trypsin 1∶2, pH 8.0, temperature 35 ℃, reaction time 4 h. Under the optimized conditions, the trypsin retained 56.1% of its activity. The range of optimum temperature and pH of the modified trypsin became wider and the heat stability and acid stability were significantly improved. These results indicated that thermal stability and pH stability of the trypsin modified by dextran can be improved, which provides theoretical basis for the modification of trypsin and expands its industrial application.