Abstract: Under semi-static water conditions, we studied the effects of single and joint toxicity of copper ion (Cu²⁺), cadmium ion (Cd²⁺) and mercury ion (Hg²⁺) on zebrafish embryonic development. The mortality rates at 48^th hour, 72^nd hour and 96^th hour as well as hatching inhibition rates at 72^nd hour, 96^th hour were used as end point of physiological toxicity, and the half lethal concentration (LC₅₀) was used as standard of toxicity evaluation. The results show that the LC₅₀s of Cu²⁺, Cd²⁺ and Hg²⁺on zebrafish embryos at 48^th hour were 0.58 mg·L^-1, 0.72 mg·L^-1 and 0.000 46 mg·L^-1; 72 h-LC₅₀s were 0.39 mg·L^-1, 1.15 mg·L^-1and 0.000 30 mg·L^-1; 96 h-LC₅₀s were 0.08 mg·L^-1, 0.19 mg·L^-1 and 0.000 18 mg·L^-1. The LC₅₀s of hatching inhibition rates of Cu²⁺, Cd²⁺ and Hg²⁺ at 72^nd hour were 0.05 mg·L^-1, 0.01 mg·L^-1 and 0.000 04 mg·L^-1, and were 0.06 mg·L^-1, 0.05 mg·L^-1 and 0.000 11 mg·L^-1 at 96^th hour, respectively. The toxicity of those heavy metal ions on zebrafish embryos was Hg²⁺ >Cu²⁺ >Cd²⁺.The toxicity of Cu²⁺, Cd²⁺and Hg²⁺on zebrafish embryos hatch inhibition rate or mortality had significant dose-response relationship, so hatching inhibition rate at 72^nd hour can be used as the most sensitive indicator for toxicity of zebrafish embryos. With a single toxic Cu²⁺, Cd²⁺ and Hg²⁺ of 96 h-LC₅₀ value, mixed unit 1 : 1 between two components at 48^th hour, 72^nd hour and 96^th hour, the combined toxicity showed synergies on zebrafish embryos; but mixed toxicity unit 1 : 1 : 1 coexistence of Cu²⁺, Cd²⁺ and Hg²⁺on zebrafish embryos at 48^th hour, 72^nd hour and 96^th hour showed toxicity antagonism.