Abstract: OBJECTIVE This text introduced an improvement of the method to synthesize iodide-diollyltrisulfide. And then it explored a method to determine the contents of iodide. METHODS Through backstreaming to synthesize iodide-diollyltrisulfide using allicin and iodude in ethanol, the product is isolated through changing the solvent. And then the contents of iodide by AgNO3 standard solution- conductometric titration after being destroyed through burning in oxygen flask were determined. RESULTS Volatilization of iodide-diollyltrisulfide was avoid when ethanol was distilled out from the system to obtain the object. The yield was increased. The determination result of the contents of iodide by AgNO3 standard solution-conductometric titration after being destroyed through burning in oxygen flask was agree with that of another method-Oxygen flask HgNO3 standard solution method.CONCLUSION The modified method can avoid the lose of iodide-diollyltrisulfide when ethanol is distilled out from the system, and make a higher yield,conductometric titration has a high accuracy and precision, which can be used to determine the contents of iodine exactly.