Abstract: A potential propylene yield model based on chemical reaction of hydrocarbon molecules to propylene for heavy oil is proposed. By combination of molecular characterization of heavy oil and reaction chemistry in catalytic cracking process, mathematic formula for potential propylene yield index is developed. By application of the model and formula, appropriate hydrocarbon types or oil feedstock for producing propylene can be sorted out and also a reference direction for hydrotreating non-ideal feedstock for catalytic cracking to maximize propylene product can be provided. Furthermore, the model and formula are applied to correlate and predict the propylene yield from vacuum gas oils and their hydrogenated gas oils including paraffinic, intermediate and naphthenic base, and the results show that the actual yield of propylene from catalytic cracking and low carbon olefins yield are raised with increase of the potential propylene yield index and good linear correlations between them are existed.