The measurement range of carbonate content in caustic soda inGB769887 was studied. First the low content measuring value was conducted based on the low measuring limit of the system, then a new measurement range of GB769887 was established. This new measurement range was further confirmed by experiments. The results of this study was further confirmed by experiments. The results if this study has greatly expanded the measurement range of GB769887, at the same time provide an effective analytical method for industrial practices. The measurement range of carbonate content in caustic soda in GB769887 was studied. First the low content measuring value was conducted based on the low measuring limit of the system, then a new measurement range of GB769887 was established. This new measurement range was the results of this study was further confirmed the experiments. The results of this study was further expanded the measurement range of GB7698-87, at the same time provide an effective analytical method for industrial practices.