In condensed phase, the dissociation mechanism of molecule is different from that of isolated molecule due to the effect of interaction between molecules. How to effectively trace the reaction process and products in condensed phase is a technical problem which needs to be solved urgently. In this paper, femtosecond transient grating spectroscopy is used to investigate dissociation dynamics in condensed phase. Transient grating spectroscopy, as a coherent spectral technique, has some advantages such as high signal-noise ratio and free background, thus it can identify trace numbers of reaction products in dissociation. The investigation about model molecules such as iodomethane and nitromethane demonstrates that the transient grating technique can observe relaxation in electronic excited state and also has ability to track reactants, products, and vibration of molecule or perssad. The dissociation dynamics in condensed phase material is significant for understanding the reaction mechanism in the fields of biochemistry and detonation. Thus the femtosecond transient grating has a wide application prospect in these fields. In addition, the transient grating technique, as a non-contact diagnostic approach, can be easily adapted to high temperature and high pressure conditions, etc. Thus, the transient grating technique also has a potential value in the fields of phase transform dynamics and high pressure synthesis, etc.