A comprehensive, real-time PAT process monitoring scheme of using near-infrared (NIR) spectroscopy, focused beam reflectance measurement (FBRM), and particle vision microscopy (PVM) was established for process characterization and process understanding of a model dynamic multicomponent pharmaceutical antisolvent crystallization system. The NIR spectra were subjected to principal component analysis (PCA) to construct the process trajectory; and the final products were characterized by X-ray powder diffraction (XRPD), raman spectrometry, and microscopy. Regardless of the PAT technique (i.e., the NIR-PCA method, the FBRM method, and the PVM method) used, this study shows that the nucleation induction time (t(ind)) increases with temperature. In addition, correlations were observed with R-2 of 0.70-0.98 between PVM method and FBRM method and of 0.58-0.84 between NIR-PCA method and FBRM method. Accounting for the dynamic nature of the experiments and changes in the liquid volume (V) as a function of time, a simplified classical nucleation theory model was derived to reveal the relationship between ln(t(ind)V) and (ln S)(-2) (S is the supersaturation ratio). Regions of very strong and very weak dependence on (ln S)(-2) were identified. Final product characterization and in-process observations of particle morphology at t = t(ind) collectively support that heterogeneous- and homogeneous-nucleation mechanisms are responsible for low S and high S regions, respectively. Therefore, the utility of an integrated-PAT approach for understanding a dynamic multicomponent antisolvent crystallization process and elucidating the nucleation mechanism was demonstrated.