The macro-instabilities (MI) in a stirred tank equipped with double eccentrically located Rushton impellers were studied by using detached eddy simulation (DES) model and PIV experimental method. By the transient simulation of the flow field, a frequency analysis was applied to the obtained time series of the velocity component. Effects of the impeller installation method and rotation direction on the MI frequency were discussed and compared with that of the single-shaft single-impeller eccentric agitation. Results show that the MI frequency of double-impeller eccentric agitation is smaller than that of the single-impeller eccentric agitation. The impeller installation method and rotation direction have obvious influence on the MI frequency of the double-impeller eccentric agitation. When the impellers are mounted on two different shafts, the MI frequency is a little larger. If the two impellers rotate in opposite directions, the frequency is larger than that of the co-rotating mode, i.e., rotate in the same direction.% 采用分离涡模型和 PIV 实验测试方法研究了双层桨偏心搅拌槽内的宏观不稳定性，通过对速度时间序列的频谱分析，讨论了搅拌桨的安装方式(单轴双桨和双轴双桨)及转动方向对宏观不稳定频率的影响，并与单层桨偏心搅拌进行了对比。研究发现，双层桨偏心搅拌的宏观不稳定频率稍低于单层桨偏心搅拌；搅拌桨安装方式及转动方向对双层桨偏心搅拌的宏观不稳定频率有明显影响：双轴双桨偏心搅拌时的频率稍高于单轴双桨偏心搅拌，搅拌桨反向旋转时的频率又高于同向旋转。
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