《说文解字》贮存的小篆，是经过整理规范、又经许慎优选并成功描写了的严密的封闭的系统。《说文》对汉字构形的系统性是自觉的，它说解了每个字的构意，贯彻了形义统一原则，并以部首为枢纽建构了构意体系。形体优选、理据重构和构意分化是《说文》部首构意体系的三大生成机制。本文以秦汉社会用字为主要参照，对《说文》部首构意体系的生成机制做全面的研究。
第一章论述《说文》部首的形体优选。其一，《说文》规整了小篆的线条，使小篆构形更为规整，构意更为明显。其二，《说文》规范了象形的形体，使其拥有确定的构形和分析。其三，《说文》厘清了字形的结构，优选得到可以分解构形、解释构意的字形，去除了社会用字中的饰笔。其四，《说文》区别了社会用字中混同的形体，彰显了不同形体之间的区别性。其五，《说文》系统地凸显了构意。每一部分都以小篆对比秦汉社会用字，举例分析。
第二章论述《说文》部首的理据重构。首先，《说文》设立了一些古文字中未独立使用的部首，使其统摄辖字的形义。其次，以构件的变化为核心，《说文》部首的理据重构又有增加构件、更换构件、离析构件、重组构件、重析象形等五个方面。其中，更换构件可以分为字形线条化、分析为省声、形近而混同等三类，离析构件可以分为《说文》受经学影响、《说文》释义为本义、《说文》释义为引申义、《说文》释义为假借义等四类。每一部分都以小篆对比甲骨文、金文、秦汉社会用字等古文字，举例分析。
第三章论述《说文》部首的构意分化。从构形分化的角度，《说文》部首体系可以分为基本部首和衍生部首两个大类，衍生部首又可以分为变形部首、加形部首、拼合部首、重合部首四个小类。本文首先归纳出辖字（不含部首）小于5个（含5个）的《说文》小部首并分类，然后分别举例考察变形部首、加形部首、拼合部首、重合部首等衍生部首和基本部首之间的构意分化。
结语部分归纳了《说文》部首构意体系的三大生成机制的特点，总结了《说文》构建部首构意体系的意义。

After being sorted out, the small seal script preserved and described in Shuowen Jiezi is a tight closed system. Shuowen is conscious of the system of the structure of Chinese characters. It explains the composing meaning of each graphic form, implements the principle of unity of form and meaning, and constructs a system of composing meaning with radicals as the hub. The optimized selection of radicals, the reconstruction of motivation and the differentiation of composing meaning are the three major generative mechanisms of the radical system in Shuowen. Taking the characters used in the Qin and Han Dynasties as a reference, this paper conducts a comprehensive study on the three generative mechanisms.
The first chapter discusses the optimized selection of radicals in Shuowen. Firstly, Shuowen regulates the strokes of the small seal script, making its structure more regular and its composing meaning more obvious. Secondly, Shuowen standardizes the form of pictographs, giving them a definite structure and analysis. Thirdly, Shuowen organizes the structure of script figures, selects the ones with the clear composing meaning, and removes excess strokes. Fourthly, Shuowen distinguishes the mixed script figures, highlighting the differences between different script figures. Fifthly, Shuowen systematically highlights the composing meaning. In each part, this paper compares the characters used in Qin and Han Dynasties with small seal script and analyzes them with examples.
The second chapter discusses the reconstruction of motivation of radicals in Shuowen. First of all, Shuowen set up some radicals which were not used independently in ancient Chinese characters, so as to control the form and meaning of characters. Secondly, with the change of component part as the core, the motivation reconstruction of radicals can be divided into five aspects. The first four aspects are adding, replacing, splitting and restructuring of component part. The last aspect is the reanalysis of pictographs. Among them, the replacement of component part has three categories: linearization of characters, phonetic symbol abbreviation and confusion of script figures. The splitting of component part has four categories. The first category is influenced by the thought of Confucian classics. The last three categories are explanations for original meaning, derived meaning and figurative sense. In this chapter, this paper compares ancient Chinese characters such as oracle bone inscription and bronze inscription with small seal script, and provides examples for analysis.
The third chapter discusses the differentiation of composing meaning in Shuowen. From the perspective of differentiation of script figures, the radical system contains basic radicals and derived radicals. Derived radicals contain deformed radicals, added radicals, combined radicals, and overlapped radicals. This paper first summarizes and classifies the small radicals with less than 5 (including 5) subordinate characters (excluding radicals), and then provides examples to examine the the differentiation of composing meaning between derived radicals and basic radicals.
The conclusion summarizes the characteristics of the three generation mechanisms of the system of composing meaning with radicals as the hub. At the same time, this paper summarizes the significance of constructing the radical system in Shuowen.