The dynamic performance of a nozzle-flapper servo valve can be affected by several fac-tors such as the disturbance of the input signal, the motion of the armature assembly and the oscil-lation of the jet force. As the part of vibrating at high frequency, the armature assembly plays a vital role during the operation of the servo valve. In order to accurately predict the transient response of the armature assembly during the vibration, a mathematical model of armature assembly is estab-lished based on the distributed parameters method (DPM) and Hamilton principle. The new math-ematical model is composed of three main parts, the modal eigenfunction, modal mechanical response expressions of the spring tube and the motion equation of the other armature assembly. After programing, the purpose of using the DPM to predict the dynamic response of different posi-tions located on the armature assembly is achieved. For verifying the validity of the mathematical model, the finite element method (FEM) and classic model (CM) of armature assembly are appli-cated by commercial software under the same condition. The comparison results prove that the DPM can effectively predict the axial and tangential deflection of the armature assembly different positions which the CM can't duing to its over-simplification. A certain error is generated when pre-dicting the axial deformation at different heights by DPM, which is caused by an approximate method to simulate the torsion of the spring tube. The comparison results of the spring tube deflec-tion at different vibration frequencies shows that the adaptability of DPM is significantly higher than the classic model, which verify the model is more adaptable for predicting the dynamic response of the armature assembly.