Abstract: Finite element method was used to design the dimensions of ultrasonic fatigue specimens of 6082-T6 aluminium alloy base material and its joints, where taking into account the effect of amplifiers (here called the holistic method). A comparison made with the dimensions of ultrasonic fatigue specimens designed by the conventional analytical method, shows that the resonant frequencies of the specimens obtained by the holistic method are closer to the test frequencies, and were almost independent of the preload and applied loads. Howerver, the stress-displacement coefficients differed significantly from those of the conventional analytical method. The ultrasonic fatigue test data of friction stir welding joints of 6082-T6 aluminium alloy at stress ratios of R = −1 and R = 0.1 were also compared and analysed by two methods. It is found that the fatigue strength obtained by the holistic method is high when R = −1, but there is almost no difference between the two methods when R = 0.1.