The relation between evaporation residue of food-contact n-hexane obturating ring and treatment parameters, which included soak method, cut method, number of cross-section, reflux temperature, and treatment after condensation, was analyzed. The results showed that soak method, reflux temperature, and treatment after condensation are main influencing factors; evaporation residue amount increases with increasing cross-section. The control levels in each sector of inspection process were put forward to ensure repeatability and authenticity of inspection result.