In this paper, the gel formation and its effect on the solution crystallization process of valnemulin hydrogen tartrate in a mixed solvent system were investigated. Some offline tools, such as differential scanning calorimetry (DSC) and X-ray powder diffraction (XRPD), and online tools, such as FBRM and PVM, were used to monitor and analyze the process. It was found that the amorphous particles of valnemulin hydrogen tartrate were first observed and then gel formation followed and finally the amorphous state particles transformed into crystalline particles. To fully understand this process, the gel formation of this compound as well as the following transformation phenomenon were investigated in detail. It was concluded that gel was temporarily formed and acted as an intermediate phase during the transformation from an amorphous state to a crystalline state.