Soda weighing method is a method to determine the content of ammonia nitrogen in water samples. Ammonia nitrogen is an important index in water quality monitoring and environmental analysis, which is used to evaluate the pollution degree of water body. Soda gravimetric method is one of the commonly used methods to determine ammonia nitrogen. Soda weighing method is to mix water samples with sodium chloride, then add a certain amount of sodium hydroxide solution and saturated lime water solution, and heat them to convert ammonia nitrogen into ammonia. Subsequently, the ammonia produced was captured by dilute sulfuric acid solution, and the content of ammonia nitrogen was determined by titration. The principle of soda ash weighing method is to make hydroxyl ions react with ammonia quickly through weighing effect, which improves the rate of ammonia escaping from water samples, thus enhancing the sensitivity of ammonia nitrogen determination. This method is simple and accurate.