In the highfrequency and overloads electrohydraulic servo loading system,the distortion and vibration of mounting rack would limit the bandwidth of system,especially in the situation of carrying out highfrequency harmonic loading,the resulted impulsive load would cause the resonance oscillation and aggravate the distortion and vibration of mounting rack,even destroy the system stability.By taking the pendulum load electrohydraulic servo loading system which adopted a cross beam as mounting rack as example,the modal and harmonic response analysis towards the structure of mounting rack was carried out using Abaqus software.By analyzing resonance oscillation characteristics of mounting rack under the effect of oil cylinder's harmonic excitation force,obtained the strength distribution of the various parts of mounting rack and the weak position of vibration zones were obtained.So,when designing the mounting rack of this system,the most important are finding the strength distribution of the various parts of mounting rack,screening out the weak position of vibration zones and conducting structural optimization.Thus the shakeproof reinforcement scheme was proposed to improve the stiffness of mounting rack,the original cross beam was changed to diagonal structure,and added the rib in the weak vibration areas and built triangular structure.The optimized schemem has made the first order inherent frequency of mounting rack raisen from 141 Hz to 190 Hz,and satisfied the bandwidth requirements of the system.