Since 2015, a working group composed of scholars and experts from both mainland China and Taiwan has been submitting proposals for the encoding of small seal script from Shuowen Jiezi to ISO/IEC JTC1/SC2/WG2. To advance the work of encoding the small seal script into Information Technology Universal Multiple-Octet Coded Character Set (UCS, ISO/IEC 10646), it is necessary to conduct an Ideographic Description Sequence (IDS) analysis of these small seal script. This paper, based on the theories of “Shuowen” studies and Chinese character Structure studies, proposes two methods for the IDS analysis of small seal script from “Shuowen”. ⑴ The rationale-based IDS analysis refers to analyzing the direct components of small seal character according to the structural meaning as explained in Shuowen, and then describing the IDS based on the planar positional relationships of the direct components. ⑵ The form-based IDS analysis refers to analyzing the basic components of small seal character according to the natural segmentation and then descrbing the planar positional relationships of the basic components. With these two methods, both the structural meaning and the form information of the small seal script are preserved. Detailed rules of the two analysisi methods are also designed to ensure the consistency of IDS analysis and description of “Shuowen” small seal script. This work could also provide a reference for the information processing of other ancient scripts.