To develop a treatment process for biological nitrogen and phosphorus in constructed wetland by natural purification system, the optimum condition of the dPAO(Denitrifying Phosphorus Accumulation Organism) was investigated in the batch experiment, and an optimum sewage treatment ratio for aerobic to anaerobic bed under the optimum condition of the batch experiment was investigated in the pilot experiment. First, the optimum condition of the dPAO was investigated to simultaneously process the biological nitrogen and phosphorus by investigating the pH value of the dPAO, the temperature, the NO3-N content, and the type of hydrogen donors based on the applicability. In addition, the optimum sewage treatment ratio of aerobic to anaerobic bed was investigated in the pilot experiment in order to apply it to an actual sewage treatment apparatus using a natural purification system under the optimum condition of the batch experiment. From the investigation of the optimum condition of the dPAO to apply a simultaneous treatment process for biological nitrogen and phosphorus using the dPAO in a sewage treatment plant with a natural purification system in the batch experiment, the optimum pH was 7, the optimum temperature was more than 20°C, the optimum content of NO3-N was more than 60mg/L, and the optimum hydrogen donor was sewage. From the investigation of the optimum sewage treatment ratio of aerobic to anaerobic bed to apply it an actual sewage treatment apparatus with a sewage treatment plant under the optimum condition in the pilot experiment, the optimum sewage treatment ratio of aerobic to anaerobic bed to simultaneously treat of biological nitrogen and phosphorus in a natural purification system was 50:50. Key words: dPAO, pH, Temperature, NO3-N, Hydrogen donor, Natural Purification System, Biological Nitrogen and Phosphorus.