The uncertainty of evaporation residue determination was evaluated using polyethylene white film for packaging of liquids on the market and 65% alcohol as soaking solution. Influencing factors of uncertainty were analyzed by experimental methods. Mathematical model of uncertainty of evaporation residue was established and all sorts of uncertainty components were calculated. The experimental results showed that the expanded uncertainty was 1.22 mg/L(k=2) and the result of determination of evaporation residue was (7.0±1.22) mg/L.