Abstract: Femtosecond pump-probe spectrometry is a powerful method that can be applied to study the dynamics of chemical bonds at the atomic level. With this technique, the ephemeral transition states of chemical reactions can be investigated in real time, and the detailed mechanism and multiple reaction paths of elementary reactions understood. A full introduction to the principle and applications of this technique in molecular ultrafast dynamics is presented. The most important research achievements based on several typical femtosecond pump-probe techniques are described. Finally, potential applications and future developments are briefly reviewed.