The Tafel equation is of fundamental importance in electrochemical kinetics, formulating a quantitative relation between the current and the applied electrochemical potential. The recent years have seen the rapid expansion and development in the application of first-principles density functional theory (DFT) simulation on electrocatalytic reactions that occur at the solid–liquid interface. This article reviews the current theoretical methods for electrochemistry modeling, in particular, those for the direct computation of Tafel kinetics of electrocatalytic reactions on surfaces based on DFT calculations. Representative reactions, namely, hydrogen evolution and oxygen evolution reactions, are selected to illustrate how the theoretical methods are applied to compute quantitatively the kinetics of multiple-step electrochemical reactions. We summarize in detail the computation procedure based on the first-principles periodic continuum solvation method for obtaining the charge transfer coefficient (CTC) and deducing the potential-dependent reaction rate. The theoretical results on the Tafel kinetics of electrochemical reactions are generalized and discussed.