对机理不清的一个系统，依据观测数据建立相应的模型，进行必要的定量研究，是 目前经济及社会许多系统面临的迫切问题。根据实际问题的需要，建模的口的大致有三 类，即１．预报；２．控制；３．结构分析。本文基于建模目的３，应用时间序列方法，依据Ｓｙｌｖｅｓｔｅｒ展开定理提出一种线性系统结构分析的算法，并给出线性系统的一个简易定阶法。 For a system with unclear mechanism, establishing the corresponding model based on the observed data and carrying out the necessary quantitative research are the urgent problems facing many systems in the economy and society at present. According to the actual needs of the problem, there are roughly three types of modeling mouth, namely 1. Forecast; 2. Control; 3. Structural Analysis. In this paper, based on modeling purpose3, a time-series method based on Sylvester expansion theorem proposed a linear system structure analysis algorithm, and gives a simple linear system order method.