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This study investigates the effects of sampling conditions on volatile organic compound (VOC) compositions including different flow restrictors, SUMMA volumes, sampling heights, and wind speeds. Results show that at the six sampling heights the concentrations of main VOC species were slightly different, while the wind speed had a greater impact on the VOC composition of source profiles. With the increase of wind speed, the weighted percentage of high-carbon aromatic hydrocarbons was higher. Besides, there was an extremely different profile between the normal production and shutdown conditions of the delayed coking unit. To compare the emission characteristics of VOCs in various process units of the S and the C refineries, the samples were collected from the catalytic cracking unit, the continuous catalytic reforming unit, and the delayed coking unit. In the continuous catalytic reforming unit, C3—C5 alkanes and low-carbon aromatic hydrocarbons were the main components collected from the S and the C refineries, accounting for 67.1％ and 34.9％, respectively. For the delayed coking unit, the total weighted percentage of high carbon C6—C12 alkanes was significantly higher than other units in the S and the C refineries, accounting for 30.5％ and 24.4％, respectively. In the catalytic cracking unit, the low-carbon C2—C5 alkanes were abundant, and the weighted percentage of propylene was higher. The emission characteristics obtained were consistent with the processing technology of production units. The results indicate that the VOC emission characteristics from the same production unit in different refineries have similarities and significant differences which are related to the technological process. The emission characteristics of VOCs could provide the data support for source apportionment work in the production units.