To develop a quantitative evaluation model for the variation of aroma harmony in processed fruit and vegetable juices, gas chromatographic data from juice samples were summed up by mathematic modeling. Based on the original fruit and vegetable juices, the total change in volatile compounds expressed in term of percentage between the treated samples by various processes and the original juice, that is, the deviation of samples, are calculated. They were then used to describe the total change of aroma compounds in the fruit and vegetable juices before and after the processing. To compare the influences of different processes on aroma harmony in fruit and vegetable juices, the samples were analyzed by gas chromatography under the same conditions and the data were obtained by comparing the deviations of the samples. The lemon juices concentrated either by freeze-concentration or by vacuum evaporation were compared against the original lemon juices. The results showed that the freeze-concentration well retained not only the absolute contents of aroma compounds but also the aroma harmony of natural lemons.