The present invention relates to the field of catalysts for polymerization, and discloses a catalyst composition for olefin polymerization, and applications thereof, and a conjugated diene monomer polymerization method, wherein the catalyst composition for olefin polymerization contains a main catalyst and a cocatalyst, the main catalyst is a double Schiff base rare earth coordination compound, the coordination compound has a structure represented by a formula (1), and the cocatalyst comprises an alkylating reagent and/or an organoboron compound. The conjugated diene monomer polymerization method comprises that a raw material containing a conjugated diene monomer contacts a catalyst composition to carry out a polymerization reaction. According to the present invention, the catalyst composition for olefin polymerization can catalyze the homopolymerization reaction of conjugated diene monomers and the copolymerization reaction between conjugated diene monomers and polar monomers; and thecatalyst composition for olefin polymerization has advantages of high conversion rate and high cis structure content in the catalysis of the homopolymerization and the copolymerization of conjugateddiene monomers. The formula (1) is defined in the specification.