目前大型汽轮发电机组轴系扭振特性的现场试验中广泛采用稳态不对称短路变频激振法。该方法能有效地测得轴系的低阶固有频率，而难于或测不到高阶固有频率。为寻求其中的原因和规律性，本文用模态分析方法，以２００ＭＷ汽轮发电机组为对象，对轴系扭振试验过程中的动态响应进行了数值仿真，计算结果与现场测试结果完全一致。研究同时表明，在一定试验参数下，高阶振型也是能够被激起的。这些结论对现场试验有指导意义 At present, the steady-state asymmetrical short-circuit frequency-variable excitation method is widely used in the field tests of the torsional vibration characteristics of large turbogenerator shaft. The method can effectively measure the low-order natural frequency of the shaft system, but it is difficult or impossible to find the high-order natural frequency. In order to find out the reasons and regularities, this paper uses the modal analysis method to simulate the dynamic response of the 200MW turbo generator during the torsional vibration test. The calculated results are in good agreement with the field test results. At the same time, the research shows that the higher-order modes can also be excited under a certain experimental parameters. These conclusions are instructive for field trials