The toxicity to Photobacterium phosphoreum of different mixture systems of sodium dodecyl sulfate (SDS) and three substituted aromatic compounds according to equiconcentration ratio of 1 : 1, as well as individual toxicity, were determined respectively. The joint toxicity was evaluated by toxicity unit (TU), additive index (AI), similarity parameter (lambda), and mixtures toxicity index (MTI). Four evaluating methods were compared and the modes of joint action of different systems were analyzed primarily. The coherent results were obtained from four different evaluating methods. Conclusions can be drawn that the binary joint effects of phenol and toluene mixed with SDS showed weak synergistic, while the other joint effects of SDS and substituted aromatic compounds were antagonistic. Of the evaluating methods, Toxic Unit is most sensitive with higher value of its parameter. Mechanisms of joint toxicity action could be discussed according to luminescence principle of Photobacterium phosphoreum and molecule structures of the mixture components.