The present invention relates to a novel group 4 transition metal compound, a preparation method for the compound, a catalyst composition comprising the compound, and a polyolefin preparation method comprising the step of performing a polymerization reaction of an olefin monomer in the presence of the catalyst composition. A group 4 transition metal compound, according to the present invention, shows an excellent catalyst activity in a polyolefin synthetic reaction as well as excellent thermal stability and thus can be used for a polyolefin synthetic reaction at a high temperature. In addition, the group 4 transition metal compound enables adjusting of the weight average molecular weight of a synthesized polyolefin and the octane content of the polymer, by varying the types of a center metal and a ligand, and thus can be utilized for polyolefin synthesis in which the grade has been adjusted.