The present invention relates to a Ni-based catalyst for preparing syngas and a tri-reforming reaction of methane using the catalyst, particularly to a Ni-based catalyst, where an active ingredient (a nickel) is impregnated in a zirconia support and the zirconia is doped with a yttrium and a metal selected among a lanthanum and an alkaline earth metal to distort the crystal lattice of the zirconia, to facilitate the transfer of oxygen ion and to increase the storage and supply of oxygen, thus inhibiting the carbon deposition on the active nickel metal and maintaining the activity of the catalyst. Particularly, if the catalyst herein is used for the tri-reforming reaction of methane where a mixture of carbon dioxide, oxygen and steam is used as an oxidant, the molar ratio of hydrogen and carbon monoxide (H2/CO) in the syngas may be selectively controlled.