<p>The need for ultraprecision smoothing strategies has been highly emphasized in modern society, and demanding requirements have posed unprecedented challenges to current precision manufacturing techniques. The Gas Cluster Ion Beam (GCIB) is a newly developed technology for materials processing. It is easy to prepare, environmentally friendly, and offers high processing accuracy and efficiency, thus garnering considerable interest and widespread application. This paper provides a comprehensive overview of the GCIB processing technology, emphasizing surface smoothing applications. It reviews various materials processed using GCIBs and analyzes the role of GCIB parameters and their effects on materials processing. Besides, the paper discusses the potential application prospects and future directions of the GCIB technology, and key conclusions and insights are identified. The discussion also includes an evaluation of the challenges and limitations associated with the GCIB, offering a balanced perspective on its practical implementation. Overall, this paper provides a thorough understanding of the GCIB technology and its role in advancing the field of surface smoothing.</p>