The invention relates to the technical field of mixed gas preparation, in particular to a preparation method of mixed gas containing free residual chlorine and used for treating COVID-19. The method comprises the following steps: taking a beaker, and cleaning the beaker for later use; pouring an aqueous solution of free residual chlorine into the cleaned beaker; pouring distilled water into the beaker to dilute the aqueous solution of free residual chlorine; carrying out full stirring by adopting a stirring rod to fully mix the aqueous solution of free residual chlorine with the distilled wate...
