Electrocatalytic water splitting is a promising approach for clean hydrogen fuel production to satisfy the needs of sustainable and renewable energy. Many efforts have been devoted to developing efficient and economic technologies for water splitting. Theoretical identification and understanding of catalytic active sites at the atomic level are essential for advancing overall water splitting technologies. This chapter briefly introduces the density functional theory (DFT) method applied in this developing field. Using some examples from recent studies, the principles and applications of the computational hydrogen electrode (CHE) method for identifying and understanding the active sites of electrocatalytic hydrogen evolution reaction and oxygen evolution reaction are discussed. This chapter further highlights the approaches beyond the CHE method due to the challenges caused by the complexity and the dynamic nature of the water splitting processes in electrified electrode–electrolyte interfaces.