In order to establish an economical and simple method to kill Enteromorpha prolifera which competitively grow together with Porphyra haitanensis in the Porphyra cultivation net, the blades of P.haitanensis and E.prolifera in different sizes were treated with direct refrigeration and acid. The results showed that there were significant differences in cell survival rates of the young blades (1-2 cm) between P.haitanensis and E.prolifera which were directly refrigerated for 5 days. The cell survival rate of the former was 90% and the latter was 50%. The blades of P.haitanensis grew well except that some dead cells appeared in the blade head after recover culture for 30 days, but the blades of E.prolifera became yellow and died gradually. When the blades grew up to 5 cm, they were treated with citric acid (pH=2.0) for 3 min the cell survival rate of P.haitanensis was about 90.9%, whereas it was only 58.5% for E.prolifera. The growth inhibition appeared in the blades of E.prolifera but not in P.haitanensis. It was better to treat them with hydrochloric acid solution (pH=2.3). After treatment for 1 min, the cell survival rate of E.prolifera was less than 20%; however, it was still up to 97% for P.haitanensis. Refrigerating the small blades (1-2 cm length) and treating the bigger blades (5 cm length) with acids would be a good method to get rid of E.prolifera.