The invention provides a method for preparing phosphorous acid and hydrogen chloride in an inner circulation tower by using phosphorus trichloride. The method comprises the following steps of: intermittently or continuously adding the phosphorus trichloride to the inner circulation tower, and then making the phosphorus trichloride react with a water solution in the tower to prepare a phosphorous acid water solution and a hydrogen chloride gas with large scale and high efficiency and yield and smoothly export the hydrogen chloride gas and heat. The method has the advantages of high reaction conversion rate and yield, steady reaction, high safety and the like and can be used for continuous production.