The lithium���sulfur battery is regarded as one of the promising energy-storage devices beyond lithium-ion battery due to its overwhelming energy density. The aprotic Li���S electrochemistry is hampered by issues arising from the complex solid���liquid���solid conversion process. Recently, tremendous efforts have been made to optimize the electrochemical reaction in Li���S batteries through rationally designing compositions and structures of cathodes. However, a deep and comprehensive understanding of the actual mechanisms of Li���S batteries and their impact on the performance is still insufficient. The vigorous development of various electrochemical analysis and in situ techniques establish a bridge between the microstructure of components and the macroscopic electrochemical performance, thus providing more scientific guidance for the optimal design of Li���S batteries. In this review, based on insights into the mechanism of aprotic Li���S electrochemistry with the aid of in situ characterization and electrochemical methods, the advanced innovations in optimizing Li���S batteries are systematically summarized, including the materials design, cathode configurations optimization, and electrolyte engineering, with the aim to gain a comprehensive understanding of cathodic redox processes and thus achieve high-performance Li���S batteries. The current status and possible future directions of the field are accordingly outlined.