Abstract: Methods in the acute toxicity test of cadmium (Cd2+) were explored by using Hydra sinensis.The median effective concentrations of Cd2+ by feeding inhibition experiment in 10min (10min-EC50) and median lethal concentrations (LC50) of Cd2+ were determined in hydras cultured in tap water,non-EDTA culture solution (NEC),and culture solution with EDTA (HEC) in 24h,48h and 72h,respectively.As a result,predation rates of the control group cultured in tap water,NEC and HEC in 10 min were 94.17%,94.66% and 51.90%,respectively.The 10min-EC50s of the tap water group and NEC group were 0.991 mg/L and 4.300 mg/L respectively.LC50s of Cd2+ in hydras cultured in tap water,NEC and HEC in 24h were 0.138 mg/L,0.330 mg/L and 0.473 mg/L,respectively; in 48h were 0.046 mg/L,0.080 mg/L and 0.203 mg/L,respectively; in 72h were 0.036 mg/L,0.040 mg/L and 0.307 mg/L,respectively.The results indicated that HEC was unsuitable for culturing Hydra and carrying out the toxicity test of heavy metals as HEC inhibited hydra’s feeding behavior and had the chelating effect for heavy metal as well.The tap water was also unsuitable for carrying out the toxicity test because the water from different cities could not reach the same quality standard.By comparison,NEC was the suitable culture solution to carry out the toxicity test of heavy metals in hydras and 10min-EC50 was the best method for toxicity test of Cd2+ due to the characteristics of simpleness and convenience.At last,as H.sinensis can easily be identified and reproduced,it was proposed here as a model organism for toxicity test of heavy metals.