This paper presents the design of a pendulum-like adaptive tuned vibration absorber (ATVA) and its application to a multi-mode system. The natural frequency of the pendulum-like ATVA can be adjusted in real time by adjusting its geometric parameters. The principle and the dynamic property of the ATVA are theoretically analyzed. Based on the analysis, a prototype of the ATVA is proposed and developed. Simulations are carried out to predict the effectiveness of the ATVA when applied to the multi-mode system. The simulated results are verified by experimental studies, which are conducted on a multi-mode platform that comprises mass, isolator, and a flexible base. The results indicate that the ATVA installed on an optimized location in the system can effectively reduce vibration over a broad frequency range and can perform better than a tuned vibration absorber.