Using Vibrio qinghaiensis sp.-Q67 (Q67) as the test organism, the concentration-response relationship of four pesticides（baygon, metalaxyl, dodine and simetryn） and their mixtures were investigated using the microplate toxicity analysis method. A quarternary pesticide mixture system with seven different concentration-ratios of the components was designed using the uniform design ray method. The obtained concentration-response data were fitted using the nonlinear least square method. A standard additive model, the concentration additivity model (CA), was used as a reference to analyze the mixture toxicity interactions. The results showed that the toxicity order of the four pesticides to the photobaterium Q67 was: dodine (pEC50 =5.35)﹥simetry (pEC50 =3.56)﹥metalaxyl (pEC50 =3.18)＞baygon(pEC50 =3.00). The pesticide dodine showed the highest toxicity and others had the similar toxicity. Toxicities of the seven rays in the quaternary mixture system positively correlated with the concentration ratios of dodine and simetryn, especially the sum of their concentration ratios (R=0.8729, RMSE=0.076) that were negatively correlatd with the sum of concentration ratios of baygon and metalaxyl (R=0.8729，RMSE=0.076). CA would be a good prediction for the toxicity of the seven quaternary pesticide mixture rays and would display a classical additive action.