The molecular dynamics in the low-frequency region (0-500 cm(-1)) sensitively reflects the intermolecular interactions in a liquid. The second harmonic generation-based coherent vibrational spectroscopy (SHG-CVS) was developed to monitor the low-frequency dynamics of molecules at a liquid interface, which was difficult to access by using the present spectroscopic techniques such as sum frequency generation or attenuated total reflection (ATR)-IR. Background-free detection with the transient grating (TG) optical configuration was adopted to obtain the weak signal under the electronically nonresonant pump condition. It was demonstrated that the SIN ratio of the SHG-CVS with the TG configuration was remarkably superior to that with the conventional time-resolved SHG configuration, and the improved detection limit enabled us to detect the low-frequency dynamics of coumarin 314 molecules at the air/water interface under the electronically nonresonant pump condition.