The invention provides a preparation method of a Ru/CeTiOx catalyst for a low-temperature SCR (selective catalytic reduction) reaction and belongs to the technical field of preparation of composite oxide supported precious metal type low-temperature SCR catalysts. According to the preparation method, soluble precursor salt of Ce and soluble precursor salt of Ti in a certain mass ratio are dissolved and mixed uniformly; a mixed solution is precipitated with a precipitant, left to stand for aging, dried and calcined, and CeTiOx composite oxide is obtained; 0.01wt%-2wt% of a precious metal Ru is supported with an equivalent-volume impregnation method; the Ru/CeTiOx catalyst is obtained after drying and calcination. The preparation process is simple, reaction conditions are mild, and the prepared Ru/CeTiOx catalyst has a large specific surface area and high low-temperature SCR denitration activity.