Toxic of Pb²⁺, Cd²⁺, Hg²⁺, Pb²⁺+Cd²⁺, Cd²⁺+Hg²⁺, Pb²⁺+Hg²⁺ and Pb²⁺+Cd²⁺+Hg²⁺ were investigated using luminescent bacteria test. The joint toxicities of heavy metals mixtures were assessed by toxic unit method and additive index method. Results showed that the joint toxicity of Pb²⁺ with Cd²⁺ was synergetic in action while the joint toxicities of Cd²⁺with Hg²⁺, Pb²⁺ with Hg²⁺, and Pb²⁺ with Cd²⁺, Hg²⁺were antagonistic.