Abstract: The effect of nickel deposit on the surface property and the catalytic cracking behavior of zeolite catalyst is studied with TPD, low temperature adsorption of nitrogen, XRD, TEM, etc. in the cracking reaction of diesel oil.It is proved that the numbers of acid sites, surface area and crystallinity of zeolite catalyst decrease as the amount of nickel deposit increase in the condition of high temperature steam treatment. As a result, cracking activity reduces and hydrogen and coke yields raise over the nickel-contaminated cracking catalyst. Experimental results showed that the size of metallic nickel particle is increased and the degree of dispersion of metallic nickel on catalyst is reduced by high temperature hydrothermal pretreatment. Therefore, the activities of producing hydrogen and coke are partly inhibited and eliminated.