《中国图书馆图书分类法》(以下简称《中图法》)修订后成为一部体系完整、类目设置精细,适应科学发展规律的类分图书的工具书。《中图法》第三版申请作为国家标准在全国实行,是我国文献分类走向统一的起点。这将使我国图书情报事业的发展,文献标准化建设,资源共享的网络化朝着更科学、更系统、更正规的方向迈进。本文就《中图法》二、三版“S农业科学”进行比较,看看三版的突出特点。一、拓扩空间,类分群书三版修订原则是在二版体系结构、标志符号不变的前提下进行增、删、改。比较二、三版,不难看出不论是页码、类目,还是注释条款、专用复分表等三版都有明显增加(如下表),其中,农业科学类的这一特点更为突出。首先,总页数增加85页,而在22个大类中S The Chinese Library of Library Classification (hereinafter referred to as “CLC”) has been revised to become a reference book with complete system, detailed classification and adaptation to the law of scientific development. The application of the third edition of “Chinese Library Classification” as a national standard in the whole country is the starting point for the unification of our country’s document classification. This will enable the development of library and information services in our country, standardization of documents and networking of resource sharing toward a more scientific, systematic and regularized direction. This article compares the second and third editions of “Chinese Agricultural Science” of “China Library Classification” to see the salient features of the third edition. First, the expansion of space, classification group book revised version of the three principles in the second edition of the structure, the same symbol under the premise of increase, delete, change. Comparing the second and third editions, it is easy to see that the three editions of page numbers, categories, and commentaries have all increased significantly (Table 3 below). Among them, this feature of agricultural sciences is even more prominent. First, the total number of pages increased by 85 pages, while in 22 categories S