在目前的桥梁移动荷载识别方法研究实践中,都因袭了正分析中采取的模态截取的概念确定模态阶数。因为不恰当的模态截取会干扰和妨碍识别,甚至会因为严重的数值病态而使得识别无法进行。为此文章在对模态反分析的过程推导的基础上引进模态选取的概念,并提出了桥梁移动荷载识别中模态选取的准则和相应的公式。 In the current research on bridge load identification method, the modal order is confirmed by the concept of modal interception in positive analysis. Because improper modal interception can interfere with and prevent identification, identification can not even be done because of serious numerical illnesses. In this paper, the concept of modal selection is introduced on the basis of deducing the process of modal analysis, and the criteria and corresponding formulas of modal selection in bridge load identification are proposed.