The invention relates to a heavy-oil cracking catalyst and a preparation and application method thereof. The catalyst contains modified ultrastable Y-type zeolite and a composition, wherein the composition contains 45-94.9 percent of rectorite and 5-50 percent of first heatproof inorganic oxides by weight percent and 0.1-20 percent of assistant selected from compounds of Mn, P and Ce by element weight percent; and the ratio of silicate to aluminum of modified ultrastable Y-type zeolite is 6-15, the lattice constant is 2.440-2.458nm, and secondary holes with aperture of 80-100 account for 30-60 percent of the total secondary holes. The preparation method of the catalyst comprises that the composition is prepared, the composition and the modified ultrastable Y-type zeolite are mixed and are crushed into slurry, and the slurry is spayed and dried. The anti-metallic contamination capacity of the catalyst is high, the coke selectivity is good, the catalyst can be used for heavy-oil catalytic cracking, the heavy-oil conversion rate is high, the gasoline yield is high and the total yield of liquefied gas, gasoline and diesel is high.