By using black and white bottles, the authors determined the effects of onions (1mg/L、2 mg/L、5 mg/ L、10 mg/L、15 mg/L) on the pond culture water body microbes’breathing and consuming oxygen in different time slot (12h、24h、48h). The results show that onion can restrain water body microbes from breathing and consuming oxygen, and different concentration onions has different restraints, moreover, the onions with the concentration of 10 mg/L、15 mg/L have obvious restraints.