This technical brief is an experimental study, which used a water tunnel to investigate the fluidelastic instability of tube bundles with asymmetric stiffness. The natural frequency ratios (streamwise/transverse) of the tubes are 50%, 60%, 70%, and 80%, respectively. Flexible tubes are set as the following two patterns: a single flexible tube and a cluster of seven flexible tubes. The vibration data of tube bundles are collected and analyzed by a self-designed Visual Analysis System. The results show that the fluidelastic instability only occurs in the transverse direction. In the streamwise direction, the coupling effect of vibrations in both directions of the tube causes the increase of vibration amplitude, no matter in the single-flexible-tube case or the seven-flexible-tube cluster. Furthermore, reducing the natural frequency of the streamwise direction will not change the transverse critical velocity but leads to an amplitude increase caused by vortex-induced vibration. Compared to the single flexible tube, vortex-induced vibration is more likely to occur in the tube cluster with larger amplitudes.