Designing experiments to research joint toxicity of multi-heavy-metal to algal is beneficial to illuminate toxic process and mechanism of heavy metals stress algal in real environment. Chlorophyll fluorescence analysis technique and 24 factorial design method were used to design and analyze joint toxicity of heavy metal Hg2 + , Cd2 + , Cu2 + and Zn2 + to chlorella pyrenoidosa. Results show that the main effects of Hg, Cd, Cu, Zn and interaction effects of Hg* Cu, Hg* Zn and Hg* Cu* Zn influence chlorella pyrenoidosa photosynthetic fluorescence parameters Fv/Fm significantly (Sig.<0.05). The relationship between the concentration of heavy metals and photosynthesis inhibition rate was established by using multiple linear regression method. The model is as follows: y［%］=－22.557+19.926Hg+5.282Cu+0.015Zn+0.029Hg*Zn－ 0.002Hg*Cu*Zn, and it can be used to account for mechanism of heavy metals stressed chlorella pyrenoidosa. To test and verify the model by statistical method and experiment, the results show that the model can be used for estimating the joint toxicity of Hg2 + , Cd2 + , Cu2 + and Zn2 + stress chlorella pyrenoidosa in laboratory conditions.