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在应用多输入多输出频域正交多项式方法进行模态参数识别时，发现其存在一些不完善之处：１）识别振型需对重根单根情况分别作出判断和计算；２）在分析频带内系统存在重根重数与输入个数相同时，理论上振型无法识别，实际应用时识别结果有较大误差。对此进行了深入探讨，从理论上论证了出现上述问题的原因：识别过程中对矩阵进行奇异值分解，在存在重数与输入个数相同的重根时，此矩阵数值小，信噪比低，因此识别精度差。针对这些问题，对原算法进行了修正，使振型识别精度得到提高。算例与试验验证证明了所做的讨论和修正是正确的、有效的。
There are some imperfections in the application of multi-input and multi-output frequency orthogonal polynomial method for modal parameter identification: 1) to identify and select the mode shapes of single roots of heavy roots; 2) When the internal system has the same number of heavy roots and the same number of inputs, the model can not be identified in theory, and the recognition result has a big error in practical application. This paper discusses in depth the reasons for the above problems in theory: singular value decomposition of the matrix in the identification process, when there is a heavy root with the same number of inputs and the same number of inputs, the matrix has small value and low signal-to-noise ratio , So the recognition accuracy is poor. Aiming at these problems, the original algorithm is modified so that the accuracy of pattern recognition can be improved. The examples and the experimental verification proves that the discussions and corrections made are correct and effective.