A method for preparing an olefin-based polymer comprising polymerizing an olefin monomer in the presence of a catalyst composition including a transition metal compound represented by Formula 1: wherein: M is a group 4 transition metal, Q 1 and Q 2 are the same or different and independently represent hydrogen; halogen; alkyl having 1 to 20 carbon atoms; alkenyl having 2 to 20 carbon atoms; aryl having 6 to 20 carbon atoms; alkylaryl having 6 to 20 carbon atoms; arylalkyl having 7 to 20 carbon atoms; alkyl amido having 1 to 20 carbon atoms; aryl amido having 6 to 20 carbon atoms; or alkylidene having 1 to 20 carbon atoms, R 1 to R 6 are the same or different and independently represent hydrogen; silyl; alkyl having 1 to 20 carbon atoms; alkenyl having 2 to 20 carbon atoms; aryl having 6 to 20 carbon atoms; alkylaryl having 7 to 20 carbon atoms; arylalkyl having 7 to 20 carbon atoms; or a metalloid radical of a group 14 metal substituted with hydrocarbyl having 1 to 20 carbon atoms; R 1 and R 2 may be connected to each other, or at least two of R 3 to R 6 may be connected to each other to form an aliphatic ring having 5 to 20 carbon atoms or an aromatic ring having 6 to 20 carbon atoms; the aliphatic ring or the aromatic ring may be substituted with halogen, alkyl having 1 to 20 carbon atoms, alkenyl having 2 to 20 carbon atoms or aryl having 6 to 20 carbon atoms, and R 7 to R 11 are the same or different and independently hydrogen; alkyl having 1 to 20 carbon atoms; alkenyl having 2 to 20 carbon atoms; aryl having 6 to 20 carbon atoms; alkylaryl having 7 to 20 carbon atoms; or arylalkyl having 7 to 20 carbon atoms; at least two adjacent to each other of R 7 to R 11 may be connected to each other to form an aliphatic ring having 5 to 20 carbon atoms or an aromatic ring having 6 to 20 carbon atoms; the aliphatic ring or the aromatic ring may be substituted with halogen, alkyl having 1 to 20 carbon atoms, alkenyl having 2 to 20 carbon atoms or aryl having 6 to 20 carbon atoms.. M is a group 4 transition metal, Q 1 and Q 2 are the same or different and independently represent hydrogen; halogen; alkyl having 1 to 20 carbon atoms; alkenyl having 2 to 20 carbon atoms; aryl having 6 to 20 carbon atoms; alkylaryl having 6 to 20 carbon atoms; arylalkyl having 7 to 20 carbon atoms; alkyl amido having 1 to 20 carbon atoms; aryl amido having 6 to 20 carbon atoms; or alkylidene having 1 to 20 carbon atoms, R 1 to R 6 are the same or different and independently represent hydrogen; silyl; alkyl having 1 to 20 carbon atoms; alkenyl having 2 to 20 carbon atoms; aryl having 6 to 20 carbon atoms; alkylaryl having 7 to 20 carbon atoms; arylalkyl having 7 to 20 carbon atoms; or a metalloid radical of a group 14 metal substituted with hydrocarbyl having 1 to 20 carbon atoms; R 1 and R 2 may be connected to each other, or at least two of R 3 to R 6 may be connected to each other to form an aliphatic ring having 5 to 20 carbon atoms or an aromatic ring having 6 to 20 carbon atoms; the aliphatic ring or the aromatic ring may be substituted with halogen, alkyl having 1 to 20 carbon atoms, alkenyl having 2 to 20 carbon atoms or aryl having 6 to 20 carbon atoms, and R 7 to R 11 are the same or different and independently hydrogen; alkyl having 1 to 20 carbon atoms; alkenyl having 2 to 20 carbon atoms; aryl having 6 to 20 carbon atoms; alkylaryl having 7 to 20 carbon atoms; or arylalkyl having 7 to 20 carbon atoms; at least two adjacent to each other of R 7 to R 11 may be connected to each other to form an aliphatic ring having 5 to 20 carbon atoms or an aromatic ring having 6 to 20 carbon atoms; the aliphatic ring or the aromatic ring may be substituted with halogen, alkyl having 1 to 20 carbon atoms, alkenyl having 2 to 20 carbon atoms or aryl having 6 to 20 carbon atoms..