Abstract: Under the direction of theory of biological fixation and removal of manganese, the oxidation trends of Fe²⁺ and Mn²⁺ in the filter is studied. It is concluded that the oxidation of Mn²⁺ is later than that of Fe²⁺. There is no clear limit between the oxidation areas of Fe²⁺ and Mn²⁺. Fe²⁺ can be completely oxidized in the sterile filter, but because Fe²⁺ take part in the metabolism of manganese removal bacteria in biological filter, which is indispensable to keep the stabilization of the filter. Fe²⁺ and Mn²⁺ can be simultaneously removed in one biological filter. On this basis the concise process(one stage filtration) and relevant technology have been invented. A large scale biological treatment plant for iron and manganese removal has been designed in Shenyang according to the theory. The removal effect is satisfactory: Total Fe is in trace and ρ (Mn²⁺) is less than 0.05 mg/L in filtrate, which are superior to the national standard for drinking water.