The sequence distribution of polydienes is studied both theoretically and experimentally. The expressions for sequence length distribution, the probability functions for monads and dyads are derived from solving a set of kinetic differential equations on the condition of constant monomer concentration [M]. The microstructure data of polybutadiene generated by anion and Ziegler-Natta catalyst at low conversion or in the case of constant [M] show that our theory mentioned above is correct, i. e. as in the case of batch reactor, there is also an unsteady stage during the initial period of polymerization for the system of constant [M] when the sequence structures of the product vary with reaction time; then the polymerization arrives at the steady stage when the microstructures become unchanging. The sequence distribution of polydienes is studied both theoretically and experimentally. The expressions for sequence length distribution, the probability functions for monads and dyads are derived from solving a set of kinetic differential equations on the condition of constant monomer concentration [M]. The microstructure data of polybutadiene generated by anion and Ziegler-Natta catalyst at low conversion or in the case of constant [M] show that our theory mentioned above is correct, ie as in the case of batch reactor, there is also an unsteady stage during the initial period of polymerization for the system of constant [M] when the sequence structures of the product vary with reaction time; then the polymerization arrives at the steady stage when the microstructures become unchanging.