The invention discloses a test assisting device for vibrational acoustical detection of 750kV strut porcelain insulators and a test method. The test assisting device comprises a general supporting base capable of adjusting the supporting area of the bottom part and steel coupling discs for mutual coupling among insulators with different diameters, wherein an insulator fixing plate at the upper part of the general supporting base is provided with 8 long-round installing holes for fixing the insulators with different diameters; and 6 steel coupling discs can realize rigid connection of the insulators with different diameters when being combined according to different orders and different directions so as to guarantee transmission of vibrational acoustical detection signals among the insulators. The test assisting device is used for simulating the site installation condition to implement vibrational acoustical vibration-detecting experiment on a plurality of sections of strut porcelain insulators connected in series. Four porcelain insulator object test pieces are utilized for carrying out simulated detection test on artificial defects of different positions of the insulators connected in series and finding the rule of the influence on detection data caused by defected positions so as to achieve the purpose of obtaining most test data by utilizing the test pieces as few as possible.