Abstract: Based on the principle of enzyme reaction kinetics, the reaction system and conditions for the test of enzyme activity of sodium alginate lyase were studied in order to improve the test method of sodium alginate lyase. In this experiment, the enzyme activity was measured by ultraviolet absorption method, and the improved method was as follows: 300 μL of substrate solution (sodium alginate 2.2%, KCl 5 mmol/L, 0.1 mol/L Na₂HPO₄-NaH₂PO₄ buffer, pH7.0) and 50 μL of enzyme solution diluted to 2.4～30 U/mL was mixed and reacted in a 37 ℃ water bath for 20 minutes, and then the reaction was terminated with an ice bath. After the reaction solution was diluted 20 times, the absorbance was measured at 235 nm. Each substrate solution need to be removed with a new pipette tip to improve the precision, and the pipette error was less than 2%. The relative standard deviation of this enzyme activity determination method was less than 5%.