Abstract: In the present paper the reaction rate of polymerization of butadiene initiated by buiyl lithium and tetrahydrofuran was investigated and the micro-structure of polybutadiene was determined. The reactive species in the system were also discussed. The relationship of polymerization rate with respect to the concentration of the monomer was obtained: second order in the induction period and first order in the propagation period. The reactivities of the active species were evaluated and the contribu-tion of different reactive species to reaction rate and micro-structure of the polymer was also resolved.