A method for producing copolymer of ethylene and alpha-olefin that has 0.1 to 90 wt% of aromatic alpha-olefinic comonomer content, comprising: a solution polymerizing ethylene, aliphatic alpha-olefinic comonomer and aromatic alpha-olefinic comonomer under presence of C3 to C20 organic solvent and a catalyst composition including a transition metal catalyst selected from the group consisting of the following Formulae in a single reactor, or series or parallel 2nd continuous reactors: where R 21 to R 26 are each independently hydrogen atom, halogen atom, (C1-C20) alkyl, (C3-C20) cycloalkyl, (C6-C30) aryl, (C6-C30) ar (C1-C10) alkyl, (C1-C20) alkoxy, (C3-C20) alkylsiloxy, (C6-C30) arylsiloxy, (C1-C20) alkylamino, (C6-C30) arylamino, (C1-C20) alkylthio, (C6-C30) arylthio or nitro, or the R 21 to R 26 may form an aliphatic ring, and monocyclic or polycyclic aromatic ring by binding with (C3-C12) alkenylene or (C3-C12) alkylene with or without the fused ring along with an adjacent substituent; alkyl, aryl, cycloalkyl, aralkyl, alkoxy, alkylsiloxy, arylsiloxy, alkylamino, arylamino, alkylthio, arylthio of the R 21 to R 26 may be further substituted with at least one selected from the group consisting of halogen atom, (C1-C20) alkyl, (C3-C20) cycloalkyl, (C6-C30) aryl, (C6-C30) ar (C1-C10) alkyl, (C1-C20) alkoxy, (C3-C20) alkylsiloxy, (C6-C30) arylsiloxy, (C1-C20) alkylamino, (C6-C30) arylamino, (C1-C20) alkylthio, (C6-C30) arylthio, nitro and hydroxy; Cp is a cyclopentadienyl ring, or a fused ring including a cyclopentadienyl ring that can form an η 5 -bond along with a central metal, Ti, and the cyclopentadienyl ring or the fused ring including the cyclopentadienyl ring may be further substituted with at least one selected from the group consisting of (C1-C20) alkyl, (C6-C30) aryl, (C2-C20) alkenyl and (C6-C30) ar (C1-C20) alkyl; and X 1 and X 2 are methyl or Cl. R 21 to R 26 are each independently hydrogen atom, halogen atom, (C1-C20) alkyl, (C3-C20) cycloalkyl, (C6-C30) aryl, (C6-C30) ar (C1-C10) alkyl, (C1-C20) alkoxy, (C3-C20) alkylsiloxy, (C6-C30) arylsiloxy, (C1-C20) alkylamino, (C6-C30) arylamino, (C1-C20) alkylthio, (C6-C30) arylthio or nitro, or the R 21 to R 26 may form an aliphatic ring, and monocyclic or polycyclic aromatic ring by binding with (C3-C12) alkenylene or (C3-C12) alkylene with or without the fused ring along with an adjacent substituent; alkyl, aryl, cycloalkyl, aralkyl, alkoxy, alkylsiloxy, arylsiloxy, alkylamino, arylamino, alkylthio, arylthio of the R 21 to R 26 may be further substituted with at least one selected from the group consisting of halogen atom, (C1-C20) alkyl, (C3-C20) cycloalkyl, (C6-C30) aryl, (C6-C30) ar (C1-C10) alkyl, (C1-C20) alkoxy, (C3-C20) alkylsiloxy, (C6-C30) arylsiloxy, (C1-C20) alkylamino, (C6-C30) arylamino, (C1-C20) alkylthio, (C6-C30) arylthio, nitro and hydroxy; Cp is a cyclopentadienyl ring, or a fused ring including a cyclopentadienyl ring that can form an η 5 -bond along with a central metal, Ti, and the cyclopentadienyl ring or the fused ring including the cyclopentadienyl ring may be further substituted with at least one selected from the group consisting of (C1-C20) alkyl, (C6-C30) aryl, (C2-C20) alkenyl and (C6-C30) ar (C1-C20) alkyl; and X 1 and X 2 are methyl or Cl.