Abstract: Suitable dispersing agents in suspension concentrate of cyanazine and atrazine mixture were screened by flowing point test. And their concentrations in suspension were determined through mass fraction-viscosity curve. In order to select the better ratio of different adjuvants the experiment was conducted by the orthogonal design. According to the layered rate and suspensibility of different combinations the better formulation was found. The storage experiment and control experiment on weed in corn field was also carried by this formulation. The results indicated that the orthogonal design could reduce the experimental time and cost, so it is an ideal method for the studying of pesticide formulation.