Abstract: Three VGO samples from different base of crude oil and processing mode were selected as feedstocks to study their catalytic cracking performance by a fixed fluidized bed device (ACE). The hydrocarbon compositions of feedstocks and their cracked products were determined by GC/MS. Test results were analyzed by using conversions with two definitions (221 conversion and 20+ conversion). Results show that the conversion of VGO feedstock mainly depends on its intrinsic properties and hydrocarbon compositions. However, using 20+ conversion to express the essential distinctions of selectivities to cracked products among various VGO feedstocks is rather better than using traditional 221 conversion. Due to the difference in product distributions and compositions of these VGO feedstocks, suitable product scheme for individual VGO feedstock should be varied.