Abstract: In this paper, the problem of identifying transfer functions in the vibration system with multiple degrees of freedom is dealt with. According to its input-output structure, such system is a multiple crossed closed loop system. By mode analyzing technique, it is required to solve an eigenvalue problem on the state equation of the degree of 2n. As n increases, tile computational demand for mode analyzing technique will increase greatly and the accuracy of parameter estimation will decrease. A method which can unifiedly deal with every stage's identification for a second order vibration system, and identify all transfer functions in the system is presented. The simulation results show that the method is simpler and more convenient than the mode analyzing technique for this class of systems.