计算大型结构的最低几阶自振频率和相应的振型是结构振动计算中必不可少的内容。为了能迅速、稳定地求出其自振频率ω及相应振型，文中通过一个典型算例阐述了改进的逐阶滤频法，即在予先假设的很不准确的振型基础上，使用迭代与正交化交替进行的方法能够得到较好的计算结果。最后还给出了计算程序总框图． The calculation of the minimum order natural frequencies and the corresponding mode shapes of large structures is an indispensable element in the structural vibration calculation. In order to obtain the natural frequency ω and the corresponding mode shapes rapidly and stably, a modified example of the filtered filter method is presented in this paper. That is, based on the previously inaccurate vibration modes, Iteration and orthogonalization of alternative methods can get better results. Finally, the calculation block diagram is given.