Abstract: The waveguide absorber (WGA) based on spiral acoustic black hole is a new configuration proposed to solve the problems of thin tip thickness and high cut-off frequency of acoustic black hole. The design method, energy dissipation mechanism and vibration reduction application effect of WGA need further research. Based on geometric acoustics theory and Euler-Bernoulli beam theory, this study proposes a design method for WGA, constructs a theoretical model for selecting material parameters and geometric parameters of WGA, reveals the influence law of WGA design parameters on the imaginary part of bending wave wave number by numerical simulation, clarifies the regulation mechanism of geometric parameters on the cut-off frequency, and further analyzes the bending wave dissipation mechanism of WGA from the time domain and frequency domain perspectives. The vibration reduction experiment of stiffened plate is carried out to verify the reliability of the design method and the vibration reduction effect of WGA. The results show that the design method proposed in this study can make WGA obtain lower reflection coefficient and cut-off frequency under the condition of larger tip thickness, improve its vibration reduction effect and application range under the condition of reducing processing difficulty. The acceleration level of the stiffened plate with WGA installed can be reduced by up to 26 dB in the range of 10 ~ 1000 Hz, and the vibration reduction effect is significantly better than that of the equal mass damping layer. The new design of WGA has the advantages of easy installation, wide vibration reduction band, good low-frequency vibration reduction effect and small influence on the inherent vibration characteristics of the structure. This study provides guidance for the design of WGA and its application in structural vibration reduction engineering.