The invention discloses a TiO2 polycrystalline foamed ceramic catalyst which is of double-layer porous structure, having an outermost layer of Ti-Fe-O solid solution, a middle layer of Zr-Al-Ce-O solid solution and a core of silica gel; the molar ratio of Ti, Fe, Zr, Al, Ce and O is (2.2-3.5):(1.0-1.5):(1.4-1.8):(2.6-3.0):(0.01-0.05):(15-18). The invention discloses a preparation method of the TiO2 polycrystalline foamed ceramic catalyst and also discloses a method of using the TiO2 polycrystalline foamed ceramic catalyst to catalyze waste plastics and biodiesel to produce hydrocarbons; wasteplastics are used as hydrogen donors, a WC polycrystalline foamed ceramic catalyst is used as a hydrodeoxygenation and isomerization catalyst, and the TiO2 polycrystalline foamed ceramic catalyst is used as a catalytic modifying catalyst, and biodiesel is catalyzed in a lab fixed-bed reactor to perform hydrodeoxygenation and isomerization to obtain liquid hydrocarbon fuels by conversion.