Abstract: Thermogravimetric analysis (TG), scanning electron microscopy (SEM), physical adsorption, Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy were employed to systematically characterize the differences in the physicochemical structures of lignite and the char obtained through low-temperature pyrolysis pretreatment. The compositional characteristics of the pyrolysis tar were further analyzed using gas chromatography–mass spectrometry (GC-MS). The results demonstrate that the properties of the low-temperature pyrolysis products (200−320 ℃) are strongly dependent on temperature. Moreover, the volatile matter content and H/C mass ratio of the lignite significantly affected the tar yield and product distribution. Taking Zhaotong lignite (ZT) as an example, the char obtained from pyrolysis pretreatment at 280 ℃ exhibited the most developed pore structure. Conversely, excessively high pretreatment temperatures promoted intensified condensation of aromatic nuclei, leading to a more densely cross-linked char structure that is less favorable for subsequent thermal dissolution and depolymerization. Compared with the direct thermal dissolution of raw coal, the char pretreated at 280 °C exhibited a remarkably elevated light oil yield in its thermal dissolution products. These findings suggest that appropriate pyrolysis pretreatment can optimize the macromolecular structure of lignite, thereby facilitating the efficient release of small molecular compounds during thermal dissolution. However, when the pretreatment temperature is too high, extensive bond cleavage initiates polycondensation reactions, which result in a denser char structure and ultimately inhibit the depolymerization process. This research elucidates the influence of low-temperature pyrolysis pretreatment on the structural evolution and thermal dissolution depolymerization of lignite, offering theoretical support for the development of clean conversion technologies for lignite.