A method of preparing a conjugated diene-based polymer by continuous polymerization using two or more reactors is provided. The method of preparing a conjugated diene-based polymer includes a conjugated diene-based polymer having excellent cis 1,4 bond content and linearity, by adjusting the ratio of a polymer and a monomer in each reactor and by adjusting the retention time in a second reactor and resolving the deterioration phenomenon of physical properties, while improving productivity by reducing the contamination of the reactors.