The property of spinnable pitch is a significant factor in determining continuously and stably industrial production of pitch-based carbon fiber, and it also affects largely the performance of final carbon fiber. Generally, the synthesis method is an important means to control the property of spinning pitch. Compared to the method of thermal polycondensation, chlorination-dechlorination method can controllably synthesize spinnable pitch from the molecular dimension to improve the spinnability. However, there are few reports on the differences in the molecular structure characteristics of spinnable pitches synthesized by thermal polycondensation and chlorination-dechlorination methods, respectively. In this work, the molecular composition and structure of the spinnable pitches were determined by elemental analysis, Fourier transforms infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF-MS), and solid-state nuclear magnetic resonance (13C-NMR). The average molecular model method was used to construct the molecular model of spinning pitch. The results show that the spinnable pitch synthesized by the chlorination-dechlorination method has higher carbon content and the characteristic peaks is shown at 1 490 cm-1 and 696 cm-1 and XPS C 1s spectra at 287.1 eV in FTIR spectra. From MALDI TOF-MS and 13C-NMR analysis, spinnable pitch synthesized by chlorination-dechlorination has a higher polycondensed degree, molecular weight, and carbon aromaticity, with the average molecular weight of 857, and the carbon aromaticity of 0.87. The molecular structure of the spinnable pitch tends to be more linear in the one-dimensional direction. According to the results of characterization analysis, the molecular models of spinnable pitch synthesized by chlorination-dechlorination and thermal polycondensation were established using the average molecular model proposed by Shoolery-Budde.