The transfer matrix method in structural vibration analysis is improved. The state vector and boundary condition vector are separated, and they are linked together by an association matrix. The computation of state vector's first derivative is simplified, and the transfer matrix can be obtained easily. The parameters of constrained layer and damping layer are introduced to uncovered section and considered as constants, so the covered section and uncovered section can obtain the same dimension transfer matrix. The structural transfer matrix can be obtained by multiply every section's transfer matrix easily even if the number of the uncovered section is much.