Abstract: The effects of ZSP zeolite catalyst, Y zeolite catalyst and their mixture system on the product distribution in deep catalytic cracking (DCC) process of hydrocracking tail oil (HTO) were investigated in a fixed fluidized bed reactor, and the effects of different catalytic materials on the isomerization during catalytic cracking and on the cracking, aromatization and hydrogen transfer reaction during DCC process were explored. The isomerization index (ISOI) was proposed to characterize the isomerization degree of catalytic cracking products by the composition of gasoline distillates. The results showed that the degree of isomerization, the degree of cracking, the degree of hydrogen transfer reaction and the degree of aromatization decreased with the increase of the proportion of ZSP zeolite in the catalyst system, the isomerization index(BG1) of cracking gas in HTO was 1.13，the ISOI of gasoline was 0.83，the yield of isomerized hydrocarbons was 29.45%，the yield of ethylene was 7.22%，and the yield of propylene was 23.66%. Compared with Y zeolite, ZSP zeolite could reduce the yield of isomerization products and increased the yield of light olefins in the DCC of HTO.

Key words: deep catalytic cracking, hydrocracking, tail oil, propylene, isomerization, isomerization index