Using a transient absorption (TA) setup switching between the single and double photon pump, a reasonable model is proposed to interpret the quasi-bounded vibration motions and dissociation–ionization of CS2 based on the 3-photon absorption (3PA) around 800 nm. Besides global fitting, mathematical tools including fast Fourier transform (FFT), continuous (Morlet) wavelet transform (CWT), and principal content analysis (PCA) are successively applied to reveal the corresponding ultrafast dynamics. Inter-system crossing is demonstrated to be the key why dissociation or even ionization is able to take place at low intensity. As a result, plasma generation, filamentation and “re-absorption” reported in Ref. Zhang et al. (2019) can be interpreted with this model.