Abstract: The catalytic cracking is a chain reaction involving three steps: initiation, propagation and termination. The main reaction mechanisms are the classical cracking mechanism and protolytic cracking mechanism. The latter one can better explain the initiation step in the catalytic cracking of paraffin. The catalytic cracking of dodecane by Y zeolite was used as model reaction to investigate the mechanism of catalytic cracking and hydrogen transfer reaction in this paper. Hydrogen transfer index（HTI，defined as a ratio of the paraffin content over the olefin content in liquid products）is used to investigate the influence of Si/Al ratio, the La content and the P content on the hydrogen transfer performance. The results indicate that HTI is a convenient way to characterize the hydrogen transfer performance of the zeolites in FCC reactions, and the results were also compared with other methods.